Abstract: The authors developed the CAD design system dedicated to sport bike frame structure and introduce in detail its design concept and implementation scheme. Based on the different usages of sport bikes and the different requirements for the system by enterprises~ the frame structural analysis of two different types of bikes, the decision of basic design parameters and the analysis of the constraint conditions are all made successively so that the calculation equations and the formulas with constraint conditions are both derived. Then the Visual C+ + program is used to operate calculation adn solve formulas. The input of the original data and the oufput of calculated results are implemented through the interactive system. This design has avoided complicated calculation and long design time.