While the Chinese Constitution guarantees freedom of religious worship, government restrictions hamper some actual religious practices. Officially, only state-recognized religious institutions are allowed to exist, and repression of non-recognized groups – such as the Falun Gong movement – can be severe. Foreigners who congregate in houses of worship specifically for foreigners, on the other hand, are not subject to the same restrictions.
A friend of mine who was a lapsed Catholic actually came back to the Church while he was in China for a volunteer year. So I wouldn’t worry too much! If you’re a practicing Catholic, you should know that political and historical divisions do exist in the Catholic Church in China, stemming from the communist government’s restrictions on institutions with perceived foreign loyalties (such as the Catholic Church, because of its ties to the Pope in Rome). But the Church perseveres and thrives. In some areas tension exists between Catholic groups recognized by the government and those that are not; in other areas Catholics on the ground do not even perceive a difference between these groups. Ordinary Catholics are generally able to celebrate the sacraments and practice their religion freely.