For the bending fatigue under the random load condition, the Miner cumulative fatigue theory was analyzed qualitatively. Random amplitude fatigue load spectrum for experiments was compiled according to that gears work under the load with Gaussian distribution load spectrum. Gear bending fatigue was carried out by the method of group test under the conditions of random load on the electro-hydraulic servo testing machine. Then the P-S-N curve of bend fatigue was got under Gaussian distribution load spectrum with particular coefficient of variation. Experiments prove that fatigue life from the result of random luffing amplitude fatigue experiments is lower than that from constant amplitude fatigue experiments, in which the upper limit of fatigue loads is the mean of load spectrum. It will be not reliable to estimate the bending fatigue life of gears that in the actual service.