Abstract: Taocha Hydrological Station is the flow measurement section of Taocha canal head, which is the source of Middle Route of South-to-North Water Diversion Project. In order to improve the accuracy of ultrasonic transit time method flowmeter, this paper studied the principle and method of discharge calculation, and put forward the average velocity calculation method of multi-layer transit time method based on multiple regression. The applicability of the method was verified by using the measured discharge as a calibration sample. At the same time, based on the ADCP measurement data, optimal power index of vertical velocity distribution at Taocha Station and its influence on the accuracy of ADCP discharge measurement were analyzed. The results show that the average velocity calculation method of multi-layer transit time method based on multiple regression can improve the accuracy of discharge monitoring at Taocha Station. The vertical velocity distribution at Taocha Station conforms to power function distribution, and the optimal index is 0.1208. It is recommended to use this coefficient when using the navigation ADCP for discharge measurement, which can reduce the error of a single discharge measurement by 1% to 2%. The research results can provide reference for the selection of discharge calculation methods for online discharge monitoring and the improvement of discharge calculation accuracy.