Abstract: According to the traditional strength theory of gear, the effect of sliding friction between teeth could be neglected during calculation. Considering the limitation and flaws, the smaller gear number of teeth, normal module, helix angle, and the factor of tooth width are selected as variables in the involute helical gear's driving design, the smallest volume sum of the two gears is determined as the object function in this paper, the fuzzy reliable optimum design's mathematical model of the helical gear under the action of the friction is set up by using the fuzzy and reliable theory. The result indicates the effect is better.