Permeation characteristics of the membranes of poly(ethylene) terephthaltae(PET) and of the bleeds of PET with poly (diethylene g1ycol) terephthalate P(DEG)T were investigated under different permeation conditions. The membranes were prepared by different methods and their effects were also investigated. The changes in membrane structure due to different heat treatment procedures were studied by infrared spectroscopy. The concentration of casting solution was adjusted to 15%. A mixture of 40wt% tetrach loroethane(TEC) and 60wt% phenol was used as a solvent. The experimental results can be summerized as follows: 1) As the content of P(DEG) T in the blends and tile evaporation temperature of solvent increased, the permeation rate increased, but rejection efficiency reased. 2) As the heat treatment temlierature increased, the crystallization degree increased, consequently, the permeation rate decreased. 3) The membranes showed the best characteristics when prepared with PET-P(DEG) T(70:30) blending ratio, solvent evaporation temperature 100℃ and operating pressure 700psi.