A lithium ion electrolyte, a preparation method and application thereof are provided. The lithium ion electrolyte includes: an ester solvent, a lithium salt and an electrolyte additive, where the electrolyte additive includes a compound as shown in the following formula I. According to the electrolyte provided by the present disclosure, all components have a synergistic effect and are matched with one another, so that the electrolyte can improve the interface stability of a high-nickel positive electrode material and prolong the cycle life of a lithium ion battery and a lithium ion capacitor.