Abstract: A new viewpoint is taken that the fatigue failure of the gear under bending load is treated as a random event,and a method for predicting the gear fatigue strength reliability under bending load is obtained from researching the event.Two new random variables K_w and D_w are proposed to describe the random event of bending fatigue failure of the gear. K_w is the fatigue damage strength which indicates the inherent ability of the gear to resist the fatigue damage under bending load. D _w is the overall fatigue damage quantity which indicates the fatigue damage degree of the gear under bending load in the life span.A cumulative fatigue damage probabilistic model of the gear fatigue strength estimation under bending load is established by means of K_w and D_w .Basd on the model,a predicting method is provided for the gear bending fatigue reliability.