The paper introduces experience of selecting hydraulic calculation formula and illustrates calculation of critical velocity of flow ( or critical pipe diameter ) and friction loss of pressure pipe in tailings transport and how to select the formula with examples 介绍工程实践中,选用水力计算公式的体会,对尾矿输送中临界流速(或临界管径)和压力管道摩阻损失的计算以及如何选用公式分别作了举例说明。