Updated the thread title as this is more about being able to make the connection rather than just the luggage aspect.

What is your exact itinerary? It sounds like you are flying via ATH and the 70-minute transfer would be at ATH, rather than PEK?
Normally that would be fine as you check in at your point of origin. In this case that sounds to be a (Greek?) island served by Aegean/Olympic, however, is that first flight to ATH on a separate PNR?