You would need return trip ticket because visa's are time limited. They only operate for a specific period of time and then, just like Cinderella you turn into a pumpkin. You have to leave. The most common visas are typically a single entry (in) and good for three months stay, and then you MUST leave.
You DO NOT want to overstay your visa in China.
China is not like the USA. They do not play around. They are a serious, serious nation that is run by leaders who got there on merit. As opposed to America's leadership who got there by mob popularity.
If you overstay your visa you will be arrested, you will pay a fee (that will increase each day you overstay) and you will do hard time in prison while the money is collected. Doing time in prison in China can be problematic as you are subject to potential organ-harvesting. You do want to keep you eyes, yes? Your liver and kidneys are important to you, yes?
A round-trip ticket guarantees that you have the means to leave that nation.
Yes, there are other nations that have this requirement, and the Western backpackers that flaunt the rules. They beg on the streets, and do other things. You need to understand that China is not some 3rd tier nation. It's successful, modern, and the people obey the law here.
In Thailand, you can get away with it...perhaps...
Yes, there are numerous work-arounds. But, you should never count on them. Many people, especially Americans have this idea that China is sort of like a big version of Thailand or Indonesia, or some other nation that they have read about. But this is really not.. not the case at all.
China is a well-developed nation. maybe 10 years you might have been able to get by on this, not in today's China. You try begging or panhandling in China, and the local beggar-boss is going to put you in your place long before the police come to haul you off to jail. China is organized, and very serious about their life, their culture and their history.
China today, in 2019, is a very organized powerful nation that demands the best that you can provide. If you are willing to assist China towards greatness they will welcome you with open arms. If you are willing to integrate with their conservative traditional culture, they will also be willing to welcome you. For China is, if anything... a very conservative and traditional culture.
I strongly advise you to follow the law, and proceed with caution. If you cannot scrounge up enough for a round-trip ticket, then perhaps you need to take a good hard look at the effort that you are putting towards preparation.