三次抛物线形断面渠道收缩水深的计算需求解高次隐函数方程，不容易求解，传统的图解法或者试算法计算过程复杂，精度较低，不便于工程实际应用。通过对三次抛物线形断面渠道收缩水深的基本方程进行适当处理，得到了快速收敛的迭代公式，再与合理的迭代初值配合使用，得到三次抛物线形渠道断面收缩水深的计算公式。误差分析及实例计算表明，在一般工程常用范围内，收缩水深的最大相对误差仅为 0.16 ﹪，计算公式形式较简捷、精度较高、适用范围比较广。

The equation for calculating contracted water depth of a channel with cubic parabola cross section is a higher order implicit function equation which is not easy to solve. Due to the complex computation process and lower precision of calculation result, neither traditional graphic method nor trial calculation approach is convenient for practical application. In this paper, iterative formula with fast convergence for computing contracted water depth of a channel with cubic parabola cross section was obtained through proper transformation on basic equation. The iterative formula combined with rational initial iteration value was developed for calculating contracted water depth of a channel with cubic parabola cross section. Error analysis and calculation example indicate that, within the general engineering range, the maximum relative error of this formula is only 0.16%. The formula in this paper can provide a wide application with its simple form and relatively higher precision.