The invention provides a method for preparing a solid polymer electrolyte lithium ion battery. The method comprises the following steps: A, dissolving a high polymer into an organic solvent, and then performing electrostatic spinning to obtain a thin-layer electrostatic spinning fiber membrane on a receiver covered by an anode diaphragm; B, adding a crosslinking monomer, a lithium salt and an initiating agent into an electrolyte solvent, and mixing uniformly to prepare a precursor; C, pouring the precursor prepared in the step B into the electrostatic spinning fiber membrane, and performing curtain coating uniformly in the electrostatic spinning fiber membrane; and D, assembling a solid polymer electrolyte/electrode diaphragm and a counter electrode diaphragm into a cell, putting the cell into a shell or a bag, sealing, heating to realize in situ synthesis of the solid polymer electrolyte, and sequentially performing formation, shaping and degassing processes to prepare a formed battery. The method provided by the invention can be simultaneously used for preparing a gel/all-solid polymer electrolyte lithium ion battery, and the obtained battery is small in interface impedance, high in mechanical strength and high in safety performance.