I will arrive 26 august in beijing and depart 16 september. my first plan was to go to the tibetian regions in sichuan and do some hike, but after they closed this area i have to find another location, at least as a backup.
I've already seen beijing, shanghai, xian, guilin, zhangjiajie, lijiang, Dali and some other cities for a couple of days.
i dont like to pay a lot just to enter a "disneyland" for a day (like jiuzhaigou national park). can do this for one or two days, but not for a longer time.
What is a good location for hike in august/september expect the regions i already visited? Changbaishan could be a option, but will also be expensive.

Next trip will be to southern yunnan/vietnam, so these regions are no option now.

How about Xinjiang and Gansu?

Gansu looks not bad, Xinjiang is to far in the west. Will do the western part of later, in some years. But didnt they close Gansu for foreigners sometimes, too? Read something about that.

A while back, they didn't want foreigners to witness the poverty in Gansu, so they wouldn't let them disembark, but I know many people who simply ignored this rule (enforcement was not especially rigorous).

As for your other point, I think it would be a shame to go to Gansu without experiencing Turpan, at the very least. There are relatively fast overnight trains from Turpan to Dunhuang, and flying into Wulumuqi is far cheaper than flying to Dunhuang.

But now they check your passport when buying a ticket. Even if I ask a chinese friend to buy a train ticket for me, they need a copy of my passport.

I have a good friend in Turpan, but she live in the very west part, so it would take two days by train to go there. I planed to visit her next year and fly direct from europe to Urumqi. Its a little daft to go to beijing first and then drive all the way back.

To stay overnight in the grasland of Gansu sounds good, have to read more about that.

I think your idea of Changbaishan is a good one - when I first started reading your post, I was thinking Changbaishan would be a good fit for hiking, and it also is a very different part of China from those you've been to. I've never actually made my way out to Changbaishan, but there are other places in the region that are much less touristed and worth visiting - I spent about a week in Huanren in eastern Liaoning back in 2004, and absolutely loved it.

Seems that there are no guesthouses in the park and camping is forbidden, so have to get out the park every day and go back all the way to Songjianghe or Baihe to find a inexpensive bed. Also the 100rmb park admission + 85rmb bus fare will make this area to expensive to stay there for a long while. Could do it for 3 or 4 days, but where to go then?

If there's issue with going to parts of Gansu, it won't be the Northwest part near Dunhuang. Instead, it'll be in the Southern counties with significant Tibetan population, especially around the Labrang Monastery in Xiahe. Protests and unrest fairly common and Chinese authorities have often limited travel to that area by foreigners and even Chinese journalists.

Wait, what part of Sichuan is closed and why?

http://www.flyertalk.com/forum/18710520-post31.html

But I am searching for a backup if that area will still be closed in august so it makes not a lot sense to make a plan with another often closed area.

I did the Zhongdian-Xiangcheng-Litang-Kangding route back in 2009 and loved it. This was also a time that much of Aba was closed off to foreigners - I remember a couple of check points where my passport was checked. Anyway - this might be an option for you - my inclination is that this route tends to remain open when other Tibetan areas are closed. I didn't do much hiking on this route, other than a quick hiked up Paomashan in Kangding - Gonggashan in Sichuan is an area that would almost definitely remain open to you - and probably has excellent hiking opportunities (I didn't quite make it down there because I ran out of time on that trip).

As for other sights around Changbaishan - the entire North Korean border region seems interesting to me - Yanbian, the Koguryo tombs (a world heritage site) and scenery in Huanren, Liaoning, Dandong.

Found this site, seems very good. Complete trekking itinerary for a lot routes in china and also for a 9 days hike around Gongga Shan.
The question is if a overnight stay in the Konka Temple will be possible like they wrote, and of course if the area itself will be open.
Have to study the site to find another ideas

Currently the Sichuan-Gansu routing from Chengdu to Songpan- Zoige - Langmusi - Hezuo (Xiahe/Labrang) - Lanzhou is open. There is hiking to be done in all of these areas, and in some, horseback riding as well if you're into that. In the past few years when there was trouble in the monasteries, Xiahe/Labrang would be closed (for short periods) to foreigners, but as that's off a side road, usually the rest of the thru-route remained open. Occasionally if coming southbound from Lanzhou, there would be a checkpoint at Linxia or Hezuo that would turn foreigners around, but not from the other direction (going northbound).

I'm about to embark on another travel adventure an if things go per my current rough plan, will be going through this area southbound (backroad to Jiuzhaigou) in about 3 weeks. Probably won't do extensive multi-day hiking, but will do some day hiking and try to report on whatever I find.

Also, if you haven't researched Siguniangshan (Sichuan), you might do so. mnredfox was there last fall and posted a very useful trip report on this forum.

Minya Konka (Gongga Shan) area is reputed to be worthwhile, but also is well-known for trails that can be quite treacherous--probably an area best done with a buddy or small group rather than alone.

Ah, Aba Prefecture, lots of Tibetan stuff there. But hard to get there.

I went to Huangshan last year around the same months. It was absolutely stunning. And you see very few Westerners.

See: http://en.wikipedia.org/wiki/Huangshan