Based on the basic principles of fracture mechanics, the paper derivated the safety allowance of fatigue failure of offshore structures, and safety allowance for measuring. On this base, an first order method for calculating the probability of fatigue failure after renewing is proposed. 本文根据断裂力学的基本原理导出了海洋工程结构疲劳失效的安全余量和检测事件的安全余量,并在此基础上给出了计算更新后的疲劳失效概率的一阶方法。