A method for making a liquid separation membrane, including: (1) providing a polyvinylidene fluoride liquid separation membrane or polypropylene liquid separation membrane prepared by a thermally induced phase separation method as a substrate membrane, soaking the substrate membrane with water or a weak polar organic liquid to make membrane pores of the substrate membrane filled with the liquid, the soaking time being between 0.5 s and 1 min, and the weak polar organic liquid being indissolvable and compatible with the polyvinylidene fluoride liquid separation membrane or polypropylene liquid separation membrane; (2) coating a casting solution of polyvinylidene fluoride on the surface of the soaked substrate membrane obtained in step (1), and quickly soaking the substrate membrane in a coagulating bath heated to a temperature of 60-100° C. for curing to yield the liquid separation membrane.