The contract seal and official seal do not need to be stamped together. The official seal or contract seal on a contract has the same legal effect, but there are obvious differences. The official seal has the highest validity among all seals, and checking whether it has an official seal has become an important criterion for judging whether a civil activity is established and effective. The special contract seal is used by the unit when signing contracts with external parties, and the official seal can be used in place of the special contract seal. Article 490 of the "People's Republic of China" and the Civil Code: 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.