The invention relates to a preparation method for a gel polymer lithium ion battery. The preparation method comprises the steps of a step S11, providing a positive plate and a negative plate with required shapes; a step S12, providing a gel electrolyte precursor liquid; a step S13, enabling the gel electrolyte precursor liquid to be formed on the two surfaces of the positive plate and the negative plate, and enabling gel electrolyte membranes to be grown on the positive plate and the negative plate in an in-situ reaction manner to obtain a positive electrode complex and a negative electrode complex; a step S14, enabling the positive electrode complex and the negative electrode complex to be suspended and fixed, and moving the positive electrode complex and the negative electrode complex to be fitted and laminated to obtain a bare cell of the battery; and a step S15, processing the gel polymer cell to obtain the formed gel polymer lithium ion battery.