Nowadays, the trade develops faster and faster, more and more Chinese enterprises engages in sale of goods, China’s using trade regulations become more and more frequent. However, there must be some disputes in the sale, so that there comes to the compensation for damages. There is a limited rule to the compensation, what is mitigation rule. It operates because it is to limit the damaged party, it should not wait for the enlargement of the damages, however, what it should do is to take active steps to avoid the enlargement of damages. This rule is a balance between the two parties, also it benefits to the deep relationship between the trade parties. I will begin from the theoretical content of the mitigation, and talking about focused on the Comparison of CISG and Chinese Contract Law. Moreover, it is also important for us to learn about the beginning time, the cost problem and the burden of proof under the rule of mitigation. Additionally, according to the Article 77 of CISG, the injured party need to take reasonable action to mitigate the damage or prevent the loss from extending. However, there is still no explicit and uniform standard to judge the “easonability”in the juridical practice. So I need to focus on the case law to explain the reasonable action, what’ more, I can learn from some cases and some academic point of view. As well, I discuss about the revelation of improvement of mitigation in Chinese Contract Law by studying of the rule of mitigation in the CISG.