The traditional process of foot and ankle orthoses made of gypsum has the disadvantages of low air tightness, low production efficiency and poor comfort. In order to solve this problem, this paper uses reverse engineering combined with 3D printing technology to customize the design of the ankle foot orthosis, obtains the foot STL data, combines the reverse modeling software Geomagic studio and Rodin 4D to modify the key parts of the orthosis, uses Grasshopper to carry out lightweight design, reduces the printing cost and quality, verifies its mechanical properties through finite element analysis, uses polylactic acid to print the physical object by FDM 3D printing technology, and conducts wear tests. The results show that the maximum deviation of the model accuracy after reconstruction is 0.868 mm, and the standard deviation is 0.047 1 mm, and the model structure is accurate. Under the concentrated load of 30 N collision, the peak stress in the middle of the 2 mm thickness orthosis is 16.32 MPa, the maximum deformation is 1.49 mm, the peak stress on the right side of the lattice is 15.64 MPa, the maximum deformation is 0.78 mm, the peak stress is less than the tensile strength of PLA material, the maximum deformation is less than the thickness of the product itself by 2 mm, the mechanical strength performance meets the requirements of subsequent production design, and the physical wear test shows that the product comfort is good.