Abstract: In former design of gear strength reliability, both strength and stress approximatly dealt with normal distribution, its method had lower calculation precision. After being improved, the gear surface contact fatigue strength obeys Weibull distribution and stress obeys normal distribution, the gear bottom bend fatigue strength and stress obey logarithm normal distribution, according to the relation of average safe rate and reliability, then the gear strength reliability design and check equations can be deduced. The method has higher calculation precision.