On what law do the two parties usually sign the contract?

Legal analysis: legal recognition of factual contractual relationship. Although there are defects in the signing of the contract, as long as one party fulfills the main payment obligations and the other party accepts these two elements, the contract will be established and come into effect, and both parties will be bound by the contract.

Legal basis: Article 490 of the General Principles of the Civil Law of People's Republic of China (PRC) stipulates that a written contract shall be concluded according to laws and administrative regulations, or if it is agreed by the parties but not in written form, a written contract shall be signed but not signed and sealed by both parties. As long as one party fulfills its main obligations and the other party accepts them, the law will recognize the validity of the contract, whether it is in writing or signed and sealed.