The test research of bending fatigue strength of 38 Si Mn Mo through hardened gear is carried out by using the STRONl603 electromagnetic resonance fatigue testing machine and double teeth pulsating loading method. The grouped test method is used in the short life. The elevation and subsidence method is used in the long life,the bending fatigue life of the gear is obtained. The Monte- Carlo simulation is used to calculate ranks. On the basis of test data,the Weibull parameters and complete S- N curve are worked out according to the principle of statistic. The bending fatigue curve with the designated confidence and reliability is obtained.Then basic data for gear design is provided for the gear material.