Abstract: Electrical Vehicle is being in a period of rapid development, however, there are certain restrictions on the improvement of the mileage because of battery pack quality. A sensitivity analysis model of a body in white (BIW) for the electrical vehicle (EV) was established based on stiffness and modal analysis. Taking the minimum weight of BIW as the optimal objective, the design variable sensitivities were obtained with correlation calculation. Based on the sensitivity analysis and engineering experience, a reasonable plan was worked out for body weight reduction. The results show that, the weight of BIW can be reduced 6.2 kg without influence the performance significantly, presenting a reference for EV lightweight.