If you travel to China, you may want to fly from 1 destination to another as it's a massive country. The most used website for domestic flights is ctrip.com, they are the giant behind the new trip.com. Generally the Chinese flights you find there are cheaper than what you would find on Skyscanner (which is now owned by Ctrip) or Expedia, etc.
However, most Chinese airlines offer further in-app purchase discount. So what I normally do is to check on Ctrip which flight is cheaper/most suitable, then download the app of that airline (most of them have english versions) and buy from the app.