Polyvinylidene fluoride flat membranes are prepared via TIPS method by using DBP as diluent and DMAc or DOP as mixed diluent at 150℃ and 220℃ repectively. The water flux and structure of membrane prepared under lower and higher temperature are investigated. The result shows that water flux of membrane prepared with 10% DMAc addition at 150℃ is 28% higher than that prepared with DBP as diluent. water flux tends to decrease when the addition of DMAc is above 10%. Water flux of membrane prepared with 10% DOP addition at 220℃ is 62% lower than that prepared with DBP as diluent. At the same time, the structure of membrane is observed and the reason of formation of different structure is explained.