As long as both parties agree, the date of contract signing will not affect the legal effect if it is wrongly written or altered. According to the provisions of the Civil Code of the People's Republic of China, the contract shall come into force on the date of signature or seal by the parties to the contract. If the signing date is wrongly written, both parties shall jointly sign or seal at the altered place for confirmation, so as to avoid unnecessary disputes in the future.
 Article 18 of the Labor Law of the People's Republic of China stipulates: "The following labor contracts are invalid: (1) labor contracts that violate laws and administrative regulations; (2) labor contracts concluded by means of fraud, threats, etc. Invalid labor contracts have no legal binding force from the time they are concluded. If it is confirmed that part of the labor contract is invalid, if it does not affect the validity of the remaining parts, the remaining parts remain valid. The invalidity of a labour contract shall be confirmed by the labour dispute arbitration commission or the people's court. " It can be seen that alteration is not the reason for the invalidity of the contract.
 According to the Civil Code, a contract is invalid under any of the following circumstances: (1) one party entered into a contract by means of fraud or coercion, which harmed the interests of the State; （2） Malicious collusion harms the interests of the state, the collective or a third party; （3） Cover up illegal purpose in legal form; （4） Damage to social and public interests; （5） Violation of mandatory provisions of laws and administrative regulations. The following exemption clauses in the contract are invalid: (1) causing personal injury to the other party; （2） Causing property losses to the other party due to intentional misconduct or gross negligence. One of the parties has the right to request the people's court or arbitration institution to modify or cancel the following contracts: (1) The contract was concluded due to a major misunderstanding; （2） It is obviously unfair when concluding the contract. If one party causes the other party to enter into a contract against its true intention by means of fraud, coercion or taking advantage of the other party's difficulties, the aggrieved party has the right to request the people's court or an arbitration institution to modify or cancel the contract. If a party requests a change, the people's court or arbitration institution shall not revoke it.
 Therefore, if both parties agree to the alteration, the legal effect will not be affected.
 Legal basis
 Article 18 of the Labor Law of the People's Republic of China, the following labor contracts are invalid:
 （1） Labor contracts that violate laws and administrative regulations;
 （2） Labor contracts concluded by means of fraud, threats, etc.
 An invalid labor contract has no legal binding force from the time it is concluded. If it is confirmed that part of the labor contract is invalid, if it does not affect the validity of the remaining parts, the remaining parts remain valid.
 The invalidity of a labor contract shall be confirmed by the labor dispute arbitration committee or the people's court.