The invention discloses a polyimide blending modified spandex. The polyimide blending modified spandex is prepared from the following components in percentage by mass: 87.0 to 99.0 percent of polyurethane urea, 0.5 to 10.0 percent of polyimide, 0 to 1.0 percent of polyurethane imide and 0.5 to 2.0 percent of auxiliaries. The invention also discloses a preparation method of the polyimide blending modified spandex. The method comprises the following steps: 1) mixing polyether glycol, diisocyanate and a solvent, and performing reaction to obtain prepolymer; 2) diluting the prepolyme by using thesolvent, conducting cooling, and adding a chain extender and a reaction controlling agent and performing reaction to obtain a polyurethane urea solution; 3)adding a mixed solution containing polyimide, polyurethane imide, auxiliaries and the solvent into the polyurethane urea solution, and conducting curing to obtain a spinning spandex stock solution; 4) performing dye-process spinning on the spinning spandex stock solution obtained in the step 3) to obtain the polyimide blending modified spandex. The spandex prepared by a preparation method disclosed by the invention has good high-temperatureresistant performance, and still keeps higher breaking strength after the spandex is subjected to high-temperature dyeing and finishing treatment.