Objective Present a method for the joint optimization design of Young's modulus and thickness of shoe for diabetic foot insoles, in order to reduce plantar pressure and internal stress in soft tissues. To propose a method for the joint optimization of stiffness and thickness in the design of diabetic foot orthotics, aiming to reduce plantar pressure and internal tissue stress. Methods A finite element model of the foot was established using reverse engineering techniques. Based on the characteristics of plantar pressure distribution, the orthotic pressure regions were identified. Finite element analysis was conducted to investigate the contact mechanics, laying the foundation for adjusting the Young's modulus and thickness of materials in different regions during the optimization process. The optimal parameter combination was obtained using the optimal Latin hypercube design. Results The designed insole increases the contact area of the sole by approximately 37.55%, resulting in a reduction of peak pressure in the metatarsal and heel regions by 15.07% and 36.96% respectively. Additionally, the internal stress in the soft tissues of the heel is reduced by 20.83%, the tension in the plantar fascia is decreased by 60% respectively. Conclusions The proposed method can be used for designing customized insoles, which have a greater contact area and hold great potential in reducing diabetic foot ulcers.