The invention discloses a preparation method for a polyimide film with low water absorption. The preparation method comprises the following steps: under the protection of N2, mixing a diamine monomer A and a dianhydride monomer A in a polar solvent to obtain a flexible polyamide acid resin solution A; under the protection of N2, mixing a diamine monomer B and a dianhydride monomer B in the polar solvent to obtain a rigid polyamide acid resin solution B; under the protection of N2, co-mixing the flexible polyamide acid resin solution A with the rigid polyamide acid resin solution B, stirring, stopping reaction when viscosity of a to-be-reacted matter reaches 2000-3500 poises; and finally, adding an accelerant and a dehydrator to uniformly mix, salivating to form a film, and performing imidization treatment to obtain the polyimide film with the low water absorption. The polyimide film obtained by the preparation method provided by the invention has a water absorption rate lower than 1.2% which is far lower than a water absorption rate (2.3%-2.4%) of conventional polyimide; and meanwhile, excellent comprehensive performance such as mechanical and electrical performance is kept.