Legal analysis: The house sales contract is invalid if Party B does not sign it. The relevant laws of our country stipulate that if the parties conclude a contract in the form of a contract, the contract shall be established when both parties sign or seal it. If the parties conclude a contract in the form of letters, data messages, etc., they may require a confirmation letter to be signed before the contract is established. The contract is formed when the confirmation letter is signed. If the parties conclude a contract in the form of a contract, the contract is established when both parties sign or seal it. If the parties conclude a contract in the form of letters, data messages, etc., they may require a confirmation letter to be signed before the contract is established. The contract is formed when the confirmation letter is signed.

Legal basis: "The People's Republic of China and the Civil Code"

Article 502 A contract established in accordance with the law shall take effect from the time of establishment, but the law provides otherwise or the parties Unless otherwise agreed. In accordance with the provisions of laws and administrative regulations, if the contract should be subject to approval and other procedures, the provisions shall be followed. If the failure to go through approval and other procedures affects the effectiveness of the contract, it will not affect the effectiveness of the contract's obligations such as reporting for approval and the effectiveness of related clauses. If the party that should go through the application approval and other procedures fails to perform its obligations, the other party may request that it bear liability for violating such obligations. In accordance with the provisions of laws and administrative regulations, if the modification, transfer, termination, etc. of a contract require approval and other procedures, the provisions of the preceding paragraph shall apply.

Article 490: If the parties conclude a contract in the form of a contract, the contract shall be established when both parties sign, seal or fingerprint. Before signing, sealing or fingerprinting, one party has performed its main obligations and the contract is established when the other party accepts it. Laws and administrative regulations stipulate or the parties agree that a contract should be concluded in written form. If the parties do not use written form but one party has performed its main obligations and the other party accepts it, the contract is established.