The central bank made it clear as early as 2013 that Bitcoin is a special commodity, and individuals have the freedom to buy and sell. For example, if A and B agree on WeChat to trade one Bitcoin for 500,000 RMB, and they agree on the time and place for an online or offline transaction, this is completely legal. It's just like some people trading game equipment on forums.
Mining is also legal; the government just does not allow large-scale mining with hundreds of mining machines at small hydropower stations in the west. However, if you buy a mining machine and mine at home, it is completely legal. Of course, whether it is legal is one thing, and whether you make a profit or not is another.
Trading cryptocurrencies on foreign exchanges varies by situation. As long as you are not the type to go to the police for rights protection when you incur losses, you generally won't be bothered.
ICO is absolutely illegal; this was made clear in 2017.