The invention discloses a method for preparing a polyimide/carbon nanotube nanocomposite. The method for preparing the polyimide/carbon nanotube nanocomposite comprises the following steps: adding aromatic diamine and dianhydride into a reactor according to equal mol amount, and then adding a solvent according to a ratio of 7.5 to 10L of solvent/mol of dianhydride; at the temperature of 20 DEG C,mechanically stirring for 3 to 5 hours to obtain a polyamic acid solution; then, precipitating, forming a film and washing out the solvent; drying, shearing and grinding into polyamic acid powder; adding a 3, 3', 4, 4'-benzophenone tetracarboxylic dianhydride monomer and an aromatic diamine monomer, and adding carbon nanotube powder which is 0.5 to 3 mass percent of the mixed powder to prepare a polyamic acid/carbon nanotube solution; and obtaining polyimide/carbon nanotube nanocomposite through thermal imidization. The polyamic acid is changed into a solid from the solution, and the carbon nanotubes are uniformly dispersed in the polyamic acid and then prepared into the polyimide/carbon nanotube nanocomposite through the thermal imidization; and a good dispersing effect is achieved.