Does a one-man company have to pay social security?

Need! As long as enterprises hire employees and sign employment contracts with employees, they must pay insurance premiums to employees. One-man limited liability company is the only corporate shareholders in the company, and he is not alone. He doesn't hire employees, so he doesn't pay insurance.

A one-person limited liability company refers to a limited liability company with only one natural person shareholder or one corporate shareholders. A one-person limited liability company is referred to as a one-person company, a wholly-owned company or a joint stock limited company for short. It refers to a limited liability company in which a shareholder (natural person or legal person) holds all the capital contributions of the company.

Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.