Abstract: Based on the time-varying mesh stiffness and the Blok flash temperature theory,the influence of tooth profile modification parameters on the load sharing ratio,transmission error and tooth surface flash temperature were systematically analyzed in this paper. The optimum tooth profile modification parameters were identified under the single-objective condition. On the other side,based on the fuzzy comprehensive decision theory,the optimum tooth profile modification parameters were identified under the multi-objective condition. The correction factor X_c was proposed,and its value was also given. Then a formula was introduced for calculating the modification amount. By the comprehensive optimum parameters of tooth profile modification,the maximum amount of tooth profile modification is the X_c times of the deformation of the alternating points B or D of the single and double tooth meshing regions under the condition that the modification index is 1.43 and the modification form is long modification.