Legal analysis: If Party A does not sign the agreement, it is generally invalid. However, if Party B has fulfilled its main obligations and Party A accepts them, the contract will come into effect.

legal basis: article 49 of the civil code of the people's Republic of China. if the parties conclude a contract in the form of a contract, the contract shall be formed when all the parties sign, seal or fingerprint it. Before signing, sealing or fingerprinting, one party has fulfilled its main obligations, and the contract is established when the other party accepts it. A contract shall be concluded in writing as stipulated by laws and administrative regulations or agreed by the parties. If the parties fail to do so in writing, but one party has fulfilled its main obligations and the other party accepts it, the contract is established.