NPR is running a series on the spread of Christianity in China. (Yeh, I know it is NPR but every once in a while you have to give them a break).
No one knows exactly how many Christians there are among China’s population of 1.3 billion. There are an estimated 21 million members of the government-sanctioned Three-Self Patriotic movement, but nobody knows how many Protestants worship in unregistered house churches.
Some recent surveys have calculated there could be as many as 100 million Chinese Protestants. That would mean that China has more Christians than Communist Party members, which now number 75 million.
From My Heart, Out Of My Mind 