中文摘要：

研究了单变量独立同分布水文事件的重现期的计算原理与方法。根据事件首次发生的期望等待试验次数与连续两次事件间期望间隔试验次数的两种重现期定义，采用数学期望值和概率母函数法，系统地推导了独立同分布水文事件重现期的计算公式。结果表明，单变量独立同分布水文事件在两种定义下的重现期相等。所得计算公式具有严格的数学基础，以期为我国现行水文频率的计算提供理论支撑。

英文摘要：

The calculation principle and method of the return period of univariate and independent identically distributed hydrological event are presented. Based on two definitions of return period （the first occurrence expected waiting trials and expected interarrival trials between two consecutive events）, used mathematical expectation and probability generating function, the return periods calculation formula of independent identically distributed event are derivated. The resuhs show that the two definitions of return period have the same expression. These expressions have solid mathematical basis, and are expected to provide the theoretical bases for hydrological frequency analysis in China.