Objective A customized insole with gradient hardness is designed for people with high arch foot and other people who need decompression. When designing insole models, we are no longer only focused on the upper surface geometry. Methods In this study, a functional gradient structure was designed, which was applied to the customized insole. Porous elements with corresponding Young's modulus are used in different areas of insole The relationship between structural element parameters and modulus is studied through mechanical tests. The foot geometry and plantar pressure distribution data of volunteers were collected, and the plantar region was divided according to the pressure contour line to assemble the structural unit. Four kinds of customized insoles were designed: ordinary flat insole, optimized flat insole, ordinary full contact insole and optimized full contact insole. Through the plantar pressure test experiment, the optimization design of sub region was verified. Results The results show that the designed insole can reduce the peak pressure of high arch foot by 52.8% in static standing state and 18.43% in gait condition. Conclusions This method can be used to design customized insoles, such as functional insoles for diabetes and high arch feet, providing better decompression function. Objective to provide a reference for conservative treatment of foot diseases with decompression needs.