Is it legal for the head office to sign a contract and the subsidiary to pay social security?

Legal analysis: illegal. Because the head office and branches are independent business licenses and official seals, there is basically nothing except affiliation. The payment of social security requires the company that signed the labor contract to pay social security to employees, and it has changed from the head office to a branch office, which no longer belongs to the original company.

Legal basis: the branch established by the employer in the Labor Contract Law of People's Republic of China (PRC) (hereinafter referred to as the Labor Contract Law) and obtained the business license or registration certificate according to law can be used as the employer to conclude labor contracts with workers; If a business license or registration certificate is not obtained according to law, the employer may conclude a labor contract with the employee.