From NW website, the location in Beijing is:

Beijing
Air China First and Business Class Lounge
International Departure Hall, just past Immigration
and security checkpoint on the right.

This is a Air China club, so I guess you need a NW ticket to get in. Now that NW broke up with Air China, I wonder how long we can still do that.

The other day, I saw a NW-CO co-owned club in ORD Terminal, it is a first time I saw this.