Here’s a helpful article from Sinologist Brent Fulton at China Source (chsource.org) about why it’s so hard to get a solid, clear picture of Christianity in China, and what we do know:
The Facts about the Church in China
“Facts about the church in China may be more readily available than they were 10 or 15 years ago. But more information does not necessarily produce greater clarity. […] No matter what point one makes about…the church in China, there will likely be more than enough facts to prove it. Getting a handle on the “facts about the facts”…may be in itself a helpful step toward better understanding the church in China.”
In the article Dr. Fulton expands on these observations:
 The church in China is growing dramatically, but no one really knows exactly how much.
 The church in China is diverse, generally divided into three streams: the officially recognized church (TSPM), traditional rural house church movements, and the more recent unregistered urban churches.
 Christianity is not illegal in China. The government’s opposition to Christianity is not ideological but reflects its preoccupation with stability above all else.
 Policy doesn’t change; practice does. The Party’s religious policy has not changed substantially in 30 years. Yet as in most other areas of life in China, there is a large and growing gray area between what is legally protected and what, in actuality, is tolerated by authorities.
For more on Christianity in China, click here.