Legal analysis: When the supervision contract is signed depends on the specific circumstances. It is generally determined before the construction contract is signed, because the construction contract clearly stipulates the supervision engineer, and it is best to require the supervision unit to participate when selecting the construction unit. Of course, both parties can agree to sign at a certain time. If the parties conclude a contract in the form of a contract, the contract is established when both parties sign, seal or fingerprint the contract.

Legal basis: Article 490 of the "People's Republic of China and Civil Code" Where the parties conclude a contract in the form of a contract, the contract is 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, administrative regulations or the parties agree that a contract should be concluded in writing. If the parties do not do so in writing but one party has performed its main obligations and the other party accepts it, the contract is established.