Random-amplitude fatigue load spectrum for experiments is made according to the ubiquitous three-parameter Weibull distribution in gear transmission. Gear bending fatigue test under the random load is carried out on a MTS electro-hydraulic servo material fatigue tester by using group testing method，and the S-N curve of gear bending strength under three-parameter Weibull distribution with specific variation coefficients is obtained. The fatigue test results show the gear’s endurance life under random load is far less than that under constant load when the load submits to three-parameter Weibull distribution random load spectrum. The theoretical value of fatigue limit for gear under random load is predicated and compared with test results. The theoretical value is in accordance with the test results. Therefore，the fatigue strength of gear bending under random load can be deduced according to the load ratio coefficient of random load spectrum.