Horseshoe cross section is commonly used for open-channel flow tunnel, but the section make hydraulic calculation become difficult because of its complex. The paper gave the formulas of hydraulic elements for 6 cambered horseshoe sections through mathematical deduction. It used Chezy formula and critical flow equation to deduce the iterative formula of corresponding central angle of top arch and upper arch, then gave the calculation formula of normal depth and critical depth.The method is applied to calculate water surface profile in Qinling tunnel of Hanjiang-to-Weihe water project.The result shows that the morphology of water surface profile meet the qualitative analysis results.The calculation process is simple and reliable and can provide reference for the hydraulic calculation of other project.