This paper presents a customized design method for ergonomic products via additive manufacturing (AM) considering joint biomechanics. An ergonomic customized design model can be built based on kinesiology involving human joint biomechanics. Manifolds of the human bone can be reconstructed from X-rays, computed tomography (CT), magnetic resonance imaging (MRI), and direct 3D scanning. The conceptual and detailed design of customized products were implemented on ergonomic shoes and insoles. A lightweight lattice structure with variable porosity was generated via structural topology optimization for an ergonomic customized design. Notably, the upper surface of the custom-made insole may adhere perfectly to the plantar surface of the patient, resulting in a lower peak plantar pressure. Finite element analysis (FEA) can be employed to simulate the static or dynamic biomechanical characteristics. The conceptual ergonomic products were forwarded to the machine and fabricated via AM, driven by visual digital twin techniques. The experiments proved that a customized design suitability method for wearable ergonomic products via 3D printing is specifically tailored to the rehabilitation needs of individual customers, while consuming the least cost, time, and materials.