The invention discloses a preparation method of a composite negative electrode sheet, the composite negative electrode sheet and a lithium ion capacitor. The preparation method comprises the following steps that 1) a layer of silicone oil is coated on the surface of the negative electrode active material layer of a negative electrode sheet, and then a lithium foil is laid on the surface of silicone oil; and 2) a layer of protective film is coated on the surface of the lithium foil and rolled and then the protective film is peeled off so that the composite negative electrode sheet can be obtained. According to the preparation method of the composite negative electrode sheet, silicone oil is used for guaranteeing that the laid lithium foil is closely adhered on the surface of the negative electrode active material layer, the lithium foil is enabled to be fully calendered through rolling and folds can be avoided; silicone oil is quickly volatilized in the rolling process and almost has no residue in the composite negative electrode sheet so as to have no obvious influence on the performance of the composite negative electrode sheet; the lithium foil is enabled to form a pre-embedded layer having great uniformity and consistency on the surface of the negative electrode active material layer through rolling so that consistency of the lithium ion capacitor can be guaranteed; meanwhile, electrolyte and lithium can be quickly and fully infiltrated so that the production efficiency of the lithium ion capacitor can be enhanced.