On the basis of summarizing low-load electric vehicle frame research, taking pure electric patrol vehicle frame as research object of lightweight design, the section size parameter optimization method is adopted to achieve lightweight targets design. According to bearing capacity of the frame, a mathematical model is established, which takes the minimum mass of single longitudinal beam as objective function and the strength and stiffness as constraints condition. The initial-design frame is optimized in workbench. The results show that overall mass after optimization is reduced from 80.532 kg to 70.409 kg, and the frame mass induced by 12.6%. Then frame statics analysis before and after optimization is carried in workbench and the results show that the frame before and after optimization meets the corresponding strength and stiffness requirements under bending and torsion conditions. Finally, frame modal analysis before and after optimization shows that no resonance phenomenon occurs in the frame before and after optimization.