Ask your airline for an extra baggage allowance, some airlines even allow one extra suitcase free of charge when you ask early enough (e.g. British Airways). In other cases you might need to pay overweight charge, but at a reduced rate (e.g. KLM, Air France).
One other way is to send your baggage as “unaccompanied luggage”. We have experience with BGS (Beijing Aviation Ground Services) near Terminal 2 of the airport (BGS, right next to China Customs at the Airport in the Huoyunlu 货运路).
BGS (Beijing Aviation Ground Services), Huoyunlu 货运路 (map), Phone: +86 10 64560664
We advise you to prepare a detailed list of contents (for Customs in Europe) always stating the country of origin for your belongings and to pack your stuff in suitcases (easier and safer to transport). At BGS you can expect about 1-2 hours for the whole procedure (buying the airway bill (AWB), getting through customs, etc). Since there is a fixed handling fee (roughly RMB 500) and then another for each kilo of your baggage, so this makes sense for larger shipments (20 to 100 kg) and for people to pool their luggage together in one shipment. Also you need someone at the receiving airport (e.g. Frankfurt, Copenhagen) to pick up and handle customs for you (if you can’t do it yourself). You have to show proof that you soon leave China in order to be able to use this service. The advantage is a kilo price of roughly RMB 40-60 for a shipment that reaches home just a few days. Much paperwork, but the fastest and cheapest way to move larger amounts of important and urgent stuff to Europe.