The invention discloses a preparation method of a composite separating film filled by an interpenetrating polymer network hydrogel. The preparation method comprises the following steps of firstly, soaking a polymer membrane into a first monomer solution, fetching out, radiating under ultraviolet rays, and crosslinking, so as to obtain a first network gel composite separating film; then, soaking the first network gel composite separating film in a second monomer solution, fetching out, and performing thermal-initiation crosslinking, so as to form the composite separating film filled by the interpenetrating polymer network hydrogel. The composite separating film filled by the interpenetrating polymer network hydrogel has the advantages that the function of adsorbing heavy metal ions is realized; the heavy metal ions in water can be effectively adsorbed in the filtering and separating process; the method is simple, the efficiency is high, the operation is easy, the cost is low, the industrial production is realized, and the property of adsorbing multiple metal ions of copper, lead, mercury, zinc, cadmium, nickel and the like is excellent; the preparation can be used for the treatment of industrial heavy metal sewage, and the removal of heavy metal ions in domestic drinking water.