The paper uses the body of a low-speed electric vehicle as the research object. Firstly, the paper extracts the load time history about the junction between the body and the suspension in the way of multi-body dynamics simulation by establishing the multi-body dynamics model of the whole vehicle and simulating the condition where the fully loaded vehicle travels in B level road at 30 km/h. Secondly, the paper processes the load time history to obtain the amplitude-frequency characteristic by Fourier transformation. Thirdly, the paper analyzes the modal of body to obtain its natural frequency. As the natural frequency of the body is less than the excitation frequency at which the suspension affects the body, the paper calculates the stress time history in quasi-static method. Then the paper counts the stress time history in rain-flow method, adjusts the average of the stress according to Goodman Curve and accumulates the damage of body based on Miner’s rule. The paper predicts the fatigue life about the body of the electric vehicle according to S-N curve next. The result shows that the fatigue life about the body of the electric vehicle is 69,000 kilometers, which doesn’t meet the requirement of manufacturer. Finally, the paper optimizes the body of the electric vehicle in moving least-squares response surface method to minimize the mass of the body under the constraint of fatigue life. The optimization result shows that the mass of the body increases 11.5%, but the fatigue life about the body of electric vehicle increases from 69,000 kilometers to 304,000 kilometers. The optimized body of electric vehicle has met the design requirement.