The invention provides a flexible all-solid planar interdigital lithium ion capacitor and a preparation method thereof. A lithium ion capacitor is composed of a current collector layer, a battery material finger electrode and a double-electric layer material finger electrode and is coated with a gel electrolyte to obtain a planar interdigitated lithium ion capacitor. The preparation method comprises the follow steps: on a flexible filter membrane substrate, by means of assistance of an interdigital mask plate, a conductive layer is subjected to suction filtration to form a current collector, and then negative (positive) and positive (negative) fingers are respectively manufactured by performing suction filtration of the battery material and the double-electric layer material on the currentcollector, and then the gel electrolyte is coated, and a flexible all-solid planar interdigital lithium ion capacitor is obtained after packaging. The flexible all-solid planar interdigital lithium ion capacitor manufactured by the invention can realize size controllability and large-scale production, and has wide market application prospects.