Considering safety and lightening of intensity, the non-conservative fuzzy reliability design formulas about automobile back-axle housing were deduced by integrating probability density and function density. The forces, intensities and geometry dimension of component etc. are normal distribution, and subordinate is parabola of exponential k. Firstly, the integral change was achieved according to initial data , function imported and extent of integrated. Secondly, the number result about the non-conservative fuzzy reliability design of automobile back-axle housing with VB program in the computer was achieved by using middle-points integral calculus and Romberg integration. The results show that this program can be used in design of automobile backaxle housing for rising up level of design.  