The polyurethane/polyacrylonitrile ( PU/PAN ) and polyurethane/cellulose acetate (PU/CA) blend ultra filtration membranes were prepared based on LoebSourirajan phase transition method. The change of the structures and properties of the PU/PAN and PU/CA membranes with the heat treatment process was studied.The results showed: the water flux decreased and retention increased with the increase of heat treatment temperature of PU/PAN blend membrane, but the water flux of PU/CA blend membrane got the maximum with heat treatment temperature of 60℃ and decreased rapidly with the heat treatment temperature of 100 ℃. The interfacial microvoid structure and its influence on the properties of PU/PAN and PU/CA blend membranes were studied.