The test data of contact fatigue strength of gears for 12 kinds of material like V-Ti spheroidal graphite cast iron
38SiMnMo and 20CrMnMo etc.are presented.The pitting endurance limits σHim and S-N Curves(R=0. 99)for gears of these materials are compared. Then some conclusions about how to make σHim and ZNT Choice are obtained.