Abstract: With considering light-weight and safety of strength, integrations of both probability density and function density, the conservative fuzzy reliability design formulas for the semi-axle of agricultural vehicles were deduced, in which forces, strengths, geometry dimension of component etc. were in normal distribution and subordinate function was parabola of exponential k. First, the numeric calculation of conservative fuzzy reliability for designing the the semi-axle of agricultural vehicles using Visual Basic was conducted, and the integral transform was achieved according to initial data and function imported and integrated extent. Second, the integral calculation of the conservative fuzzy reliability of the semi-axle of agriculture vehicles was made by using middle-points integral calculus and Romberg integration. This program can be directly used in design of the semi-axle of agricultural vehicles so as to raise design level.