Using the theory of reliability design, this paper deduces the calculational equations about reliability of the tired strength of the bear surface contact and the tired strength of the bear bottom bend while its strength and strain both obey the normal state distribution of logarithm. 运用可靠性优化设计理论,推导出在齿轮强度、应力均服从对数正态分布时的齿轮接触疲劳强度和齿根弯曲疲劳强度的可靠度计算公式。