The practice of “zeroing” which effects establishing “the existence of dumping” is one of the ways to calculate “margins of dumping”. The practice of “zeroing” used to be legitimate during GATT while currently there are not specific articles about the practice of “zeroing”. It is a long time to struggle and compromise among countries showing the development of the practice of “zeroing” with cases interpretation and analysis which refers to the calculating the margin of dumping, existence of dumping, the panel reports and the Appellate Body report. With the development of international trade, trade frictions happen frequently. Some countries impose protectionist barriers aiming to China by anti-dumping measures, adopting the practice of “zeroing” to calculate “margins of dumping”, which makes china suffer great losses. The main focus in the thesis is to introduce the practice of “ zeroing” and the relationship between “ zeroing” and “existence of dumping”. Proposing strategies of maintain China’s interests during trade process by analyzing and summarizing typical cases.