Abstract: This paper based on the cooperative item of gas exploitation of Xihu trough studies one of the problem which was disputed in standard contract on oil and gas field of contract area of Xihu trough by Sino-Foreign. In the light of the especial attribute of Xihu trough, the East China Sea, relative items that are not apparently applicable to the especial attribute of Xihu trough, the East China Sea according to the basic principle of Standard Contract must be mended, and stating the significance of mending definition of oil (gas) field on basis of protecting the benefits of our country and inspiring foreigner to exploit gas field.