With the improvement of the precision of measuring robot, the precise trigonometric elevation measurement has been widely used in river-cross leveling. Based on the exact formula of precise trigonometric height measurement and the error propagation law, the formula of measurement error is derived in this paper. Controlling the height angle and measuring distance of instrument could improve the measuring accuracy and reach the second-class leveling accuracy. The present method was applied to the left and right bank elevation survey of Datengxia hydro-junction project, and results demonstrate that the method meets the requirements of second-class leveling accuracy and enhances working efficiency. The application results can be used for reference in similar river-cross leveling.