In order to solve the problem that the conventional physical separation equipment is difficult to achieve good oil removal effect caused by the serious emulsification of produced water in Nanhai oil and gas fields, based on a gas field, the methods of process improvement test and data analysis are used, and the substitution effect and oil removal effect of a new combined coalescer in different process flows are studies .Combined with the large-scale produced water system project, the comprehensive evaluation of coalescence degreaser in project implementation is compared. The results shows that the new combined coalescer has more than 95% oil removal efficiency for emulsified oil, and gradually shows its operation and maintenance advantages and economic advantages after putting into operation.