通过对弧底梯形明渠临界水深基本方程的数学变换，应用迭代理论得到其无量纲临界水深快速收敛的迭代公式；结合工程实际在大量分析计算的基础上应用最佳逼近拟合原理确定出了恰当的迭代初值，从而提出了一种简捷、准确、通用的弧底梯形明渠临界水深的简捷计算方法。

According to mathematical transformation for the basic equation on critical water depth of open trapezoidal channels with spherical bed, the paper poses an iterative formula on its calculaton by applying the iteration theory. Moreover, on the basis of a mass of calculations and analyses on practical engineerings and selecting the right initial value on the optimal approaching theory, a short - cut, correct and effective method for direct calculating the critical depth of open trapezoidal channels with spherical bed was proposed. 