Regarding the legality of cryptocurrency trading, we can discuss it from several aspects.

First, individuals can purchase USDT in China using RMB and then trade cryptocurrencies such as Bitcoin and Ethereum with USDT; this process itself is not illegal. According to Chinese laws, there is no explicit prohibition on trading cryptocurrencies. We can review several key regulatory documents:

On December 5, 2013, the People's Bank of China and other relevant departments issued a notice on preventing Bitcoin risks, clarifying the nature of Bitcoin and stating that Bitcoin is a virtual commodity, allowing the general public to participate at their own risk.

On September 4, 2017, an announcement was released by the People's Bank of China and seven other departments, clearly prohibiting illegal token issuance and financing, but not prohibiting individuals from holding, trading, or buying and selling cryptocurrencies, including stablecoins like USDT.

On September 24, 2021, the People's Bank of China and ten departments jointly issued a notice emphasizing the prevention of financial risks brought by cryptocurrencies, reminding the public to participate in virtual currency trading cautiously, but still did not explicitly prohibit individual trading.

In simple terms, individuals trading cryptocurrencies within China do not violate existing laws and regulations. It is important to note that if illegal sources of funds are involved in trading, such as fraudulent funds, then there may be certain legal risks, especially during the withdrawal process. If the source of funds is unclear, the account may be frozen.

Overall, as long as the trading process is compliant and the funds are legal, trading cryptocurrencies is not a problem.