Legal analysis: it may be effective or invalid. Whether a contract signed without official seal has legal effect depends on the specific situation: 1. If the contract is signed by the entrusted agent of the unit within the scope of its authorization or the legal representative of the unit, the contract is valid. 2. If the signed entrusted agent has no power of attorney, exceeds the power of attorney or signs a contract after the power of attorney is terminated, the signed contract is valid after ratification by the principal. Without ratification, the contract is invalid and the actor shall bear civil liability. Knowing that someone else has committed a civil act in my name without denying it is regarded as consent.

Legal basis: Civil Code of People's Republic of China (PRC).

Article 919 An entrustment contract is a contract in which the principal and the agent agree that the agent shall handle the principal's affairs.

Article 490 Where the parties conclude a contract in the form of a contract, the contract is formed when 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 written form as stipulated by laws, administrative regulations or agreed by the parties. If the parties do not do this in writing, but one party has fulfilled its main obligations and the other party accepts it, the contract is established.