The invention relates to a preparation method for a polyamide acid solution for preparing polyimide fibers, and is used for mainly solving the problems in the prior art that when a two-step method is adopted for preparing polyimide fibers, the polyamide acid solution has unstable viscosity control and too large viscosity in the preparation process to cause spinning difficulty. The problems are relatively well solved by adopting the technical schemes that the preparation method comprises the following steps: a) proportioning diamine and tetracarboxylic dianhydride according to the total molar ratio of 1 to X; b) under the protection of an inert gas, stirring diamine at low temperature to be completely dissolved in an organic solvent; and c) slowly adding tetracarboxylic dianhydride with the Y quantity ratio to the solution with the feeding time of 20-60 minutes, after the feeding is finished, continuing to carry out a reaction for 30-120 minutes, adding tetracarboxylic dianhydride with the Z quantity ratio to the reaction system, continuing to carry out a reaction for 0.5-10 hours, and thus obtaining the polyamic acid solution which can be used for industrial production of polyimide materials.