Objective To introduce the design principles and functional modules of a self-programmed software system for designing customized hip stem prosthesis based on X-ray films. Methods Some femoral anatomical feature points (e.g. the peak of trochanter minor, the center of femoral head, trochanteric fossa), two planned points on osteotomy line (a boundary point at the side of trochanter major and the lowest point on the osteotomy line), and some key location points for designing (e.g. the hip stem far-end location point, the highest point of neck shaft connecting section) were extracted from X-ray films by using image processing methods to predict the patient’s proximal femoral cavities. The customized hip stem prosthesis was designed by inputting the design parameters (e.g. the neck-shaft angle, anteversion angle, thickness of reserved cancellous bone, radiuses of the cross-section in matching area of the prosthesis, height of transition area of the prosthesis). Two-dimensional cross-section verification on matching area of the customized hip stem prosthesis and three-dimensional overall verification were conducted. Results According to the verification results, the design parameters were adjusted to regenerate point cloud data of the hip stem prosthesis model, which could make the designed hip stem prosthesis match the patient’s femoral cavity and finally meet the requirements for the customized purpose. Conclusions The program system introduced in this paper can be used to design customized hip stem prostheses for patients. With the much shorter design cycle and relatively lower cost, this program system can promote the application of customized hip stem prosthesis in clinic and further prove the life quality of patients.