Is it illegal for the owner of Heli Baoyi to let me make my own deposit?

Illegal. According to the Contract Law of People's Republic of China (PRC), a contract is an equal and voluntary agreement, and the parties shall follow the principle of honesty and credit, and there shall be no illegal acts such as fraud or coercion. It is illegal for the owner of Heli Baoyi to ask for the deposit in advance. There is no clear agreement in the contract, and the purpose and refund method of the deposit are not informed.