Western Union is one way, however, be warned that their agents in China do not always seem to be cooperative with foreigners. Unless you know the specific Agent location where the money is to be sent and picked up, sending a transfer can be a problem.
Western Union is available at most China Post branches, however, the staff at those different branches are not always familiar with the process for a foreigner to pick up money, or they may be unable to speak english at the branch.
If you do use Western Union, send the transfer to a specific China Post Branch (the main branch in a big city is best...check WU's website for addresses). Avoid sending the money to a WU agent attached to a bank in China, as they are notorious for being unhelpful, charge high exchange fees for conversions, and having bureaucratic procedures to get the money.
Avoid bank to bank transfers as the safety of the transfer can not be guaranteed due to less than trustworthy clerks...if you get my drift.
An American Express agent may offer other ways to transfer money.