The invention provides a solid polymer electrolyte doped with modified nanofiller and a preparation method of the solid polymer electrolyte and belongs to the technical field of solid polymer electrolyte materials. The novel solid polymer electrolyte doped with modified nanofiller is prepared by mixing dopamine coated silicon dioxide nanoparticles grafted with polyethylenimine on the surfaces, lithium salt, polyoxyethylene, polyethylenimine and an organic solvent capable of dissolving polyethylene oxide and then drying the mixture for film formation. The preparation method comprises the steps as follows: preparing the dopamine coated silicon dioxide nanoparticles, grafting the particles with polyethylenimine on the surfaces, preparing an electrolyte mixed solution and preparing an electrolyte film. The preparation technology is simple, high in efficiency and low in production cost, and the prepared solid polymer electrolyte for lithium ion batteries has better thermal stability and mechanical strength as well as excellent safety performance and has very bright market prospects.