As a common currency, the US dollar can be directly remitted, so it is necessary to change the Korean won into US dollars and then transfer it to China.
Korean won and RMB are not common currencies, so if you want to remit money to China through Korean banks, you can only convert it into US dollars first and then remit money.
There is a way that there used to be people from China in Yanbian, China.
For example, your family in China transfers money to their bank account in China, and then they transfer Korean won to your bank account in South Korea. On the other hand, if you know such people, you can give them won in Korea, and they will transfer RMB to your bank account in China, with high speed and high exchange rate.