To realize the lightweight design of the Formula Student China's (FSC) frame structure, the geometry optimization is performed with the concern of modal, strength and stiffness constraints. Firstly, a finite element model of the frame is built based on the FSC rules. Subsequently, five types of static characteristic analysis conditions, five types of stiffness analysis conditions of important parts and six free modal analysis conditions are conducted for performance analysis of the frame structure. The size optimization model is set up with minimizing mass as the objective, the allowable stress of materials, allowable stiffness of important parts and excitation modal of the engine as the constraints, and the frame tube thickness as the design variable. Finally, approximate solution is acquired by sequential linear programming with nonlinear optimization model. A good lightweight result is obtained. The weight of the FSC frame decreases by 5.34 kg with a reduction rate of 15.7%.