Generally speaking, a contract is valid only if it meets the effective conditions stipulated by law, otherwise it will be invalid and may be sanctioned by law. In China, it is stipulated that a contract must meet the following conditions before it can take effect and have legal effect:

First of all, both parties to a contract should have the ability to conclude a contract. In China, people with contracting ability are divided into citizens, legal persons, other economic organizations, individual industrial and commercial households and rural contracting households. In addition, in order to become the subject of a valid contract, it must be within the legal business scope agreed upon when the contract is concluded.

Secondly, the meaning of both parties to the contract is true. The expression of true will means that the actor's internal expression of will is completely consistent with the external expression of will when establishing, changing or terminating the civil legal relationship. Because people sometimes say the wrong thing intentionally or unintentionally, or say something different from what they think, which means the meaning is not true. This kind of unreality also exists in the contract, which may be intentional or completely unintentional by the parties, but it will harm the interests of the other party in any case. Therefore, in order to safeguard the interests of the parties to a contract, the law stipulates that a contract concluded under the condition of untrue expression of will is invalid or should be changed or cancelled.

According to the civil law of our country, a contract concluded by fraud, coercion or taking advantage of a person's danger is invalid. At the same time, China's civil law also stipulates that any contract that maliciously colludes and harms the interests of the state, the collective or the third party, as well as a contract that violates the law or social public interests and covers up the illegal purpose in a legal form, is also invalid. In addition, in the process of signing a contract, one party may, due to the malicious behavior of one party, request to change the contents of the contract or terminate the contract in an obvious obviously unfair way under the condition that the expression of intention is untrue or the interests of both parties are not harmed. This kind of contract mainly includes contracts signed due to major misunderstandings and contracts in obviously unfair.

In addition, the contents of the contract shall not violate the law and public interests. The subject of the contract expresses by will all matters with legal effect that the conclusion of the contract hopes to produce, and shall not violate the provisions of the law or the requirements of social public interests. Of course, if a contract includes many aspects, some of them are invalid, and the validity of other parts will not be affected.

In a word, only contracts that meet the above conditions are valid and can cause corresponding legal consequences. As for the invalid contract, it is put forward by the parties, the court decides or the court directly arbitrates, and the general contract is invalid or revoked. The contract law of our country has made the following provisions: invalid contracts and cancelled contracts have no legal effect from the beginning; If part of the contract is invalid and does not affect the validity of other parts, the other parts are still valid; After the contract is invalid or cancelled, the property obtained from the contract shall be returned. If it is impossible or unnecessary to return it, it shall be compensated at a discount. The party at fault shall compensate the other party for the losses suffered as a result. If both parties are at fault, they shall bear their respective responsibilities. If the parties collude maliciously and harm the interests of the state, the collective or the third party, the property thus obtained shall be nationalized or returned to the collective or the third party.