Legal analysis: 1. The contract is invalid without the signature or seal of the employer. What a contract needs is the signature or seal of both parties. Signature and seal have the same legal effect, only one of them is enough. But if it is a legal person, it is better to have a legal person seal.

2. If the unit only signs but does not seal or only seals and does not sign, as long as the legal representative of the unit performs his duty behavior, that is, he signs or seals the unit seal on behalf of the unit, rather than concluding a contract for his own affairs in his own name, then the contract is effective for the unit.

legal basis: according to article 165 of the civil code of the people's Republic of China, if the power of attorney is in written form, the power of attorney shall specify the name of the agent, the matters of agency, the authority and the time limit, and shall be signed or sealed by the principal.

article 49 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.