The Marriage Law provides that the no-fault party may claim damages from the party at fault. Therefore, once the extramarital affair is determined by the court, the no-fault party may get compensation. However, because the parties having extramarital affairs usually act secretly, it is difficult to get evidence, resulting in most of the parties to divorce cases involving extramarital affairs not being able to get compensation. Generally speaking, attention should be paid to the collection of the following key evidence: guarantee or repentance written down by one party reluctantly to show repentance, which is the key evidence proving extramarital affairs; police record on the prostitution events can be important evidence; after the employee's extramarital affair have been verified, the working unit sometimes may deal with the problem of his or her life style, and therefore written material handling the problem is also a kind of important evidence; the correspondence, short messages and e-mails between the two parties. For this kind of evidence, except written evidence, it is more appropriate for the short messages and e-mails to be notarized before being submitted to the court; photos, audio and video, etc. It should be noted that evidence must be obtained in a lawful way. Otherwise it will not be admitted as evidence.