Through the stress field intensity approach, the relationship between the rotary bending fatigue limit and torsion fatigue limit was studied.

Bending fatigue limit stress is still short of reliable data for gear of domestic material in gear design mostly used are the data offered from ISO6336.

Using present bending fatigue limit data of gear tooth and other materials of gears, the calculating method of re liability is proposed for bending strength of gear tooth st steady condition.