According to their new annual report from the PC Gaming Alliance (an industry trade group):

China continues to be the largest and fastest growing market for PC games with record 2012 revenue of US$6.8 billion.  Mature game markets in Korea, Japan, U.S., U.K. and Germany all showed growth in 2012. Together these markets also increased revenue in 2012, to $8.4 billion.

Altogether PC game sales reached $20 billion globally last year.  Be sure to also check out Chapter 14 for more info about the gaming and entertainment industry in China