Abstract: Using power circulating type gear tester, 33 pairs 20CrMnMo carburized and quenched gears, having tooth surface hardness HRC62, were tested to investigate the contact fatigue life. The test results were treated by statistical methods and plotted as R-S-N curve. The contact strength limits σ_Hlim were 1 571.6 N/mm² with reliability 0.99 at 5×10⁷ cystes. By using scanning electron microscope etc., the texture of tooth surface damage were described and the mechanism of failures was investigated.