The invention provides nanometer modified polyimide and a preparation system and method of the nanometer modified polyimide. The preparation system comprises a solution preparation system and a thin film preparation system, wherein the solution preparation system comprises a reaction kettle which is provided with two liquid inlets, and the liquid inlets are communicated with a dianhydride solvent tank and a diamine solvent tank respectively; the thin film preparation system comprises an imidization furnace, a winding machine and a film-drawing mechanism, and a defoaming tank is communicated with the film-drawing mechanism through a slobbering nozzle. The preparation method comprises the following steps of preparing a polyimide solution and preparing a polyimide thin film. Solid dianhydride is added into a polar solution of diamine by several times, a lot of diamine molecules are made to attack the surface of the suspending dianhydride, a polymerization reaction is quickly conducted, so that the situation that the ratio of the dianhydride to the diamine is destroyed due to the consumption caused by complexation of the dianhydride and the solvents is avoided, and a high-concentration and stable PAA solution is generated. When the polyimide thin film prepared by using the method is used, the parameters are qualified, and the quality of the finished product is excellent.