The discharge is one of the main test elements of hydrology，the traditional hydrologic method to measure water flow is to use the rotor-type current meter or the float method，which is not only laborious，but also is timeconsuming，and hazardous as well.In recent years，multi-rotor UAVs have become more and more widely used in various industries.DJI UAVs were applied by Gan River＇s Upstream Hydrology and Water Resources Monitoring Center for technical research，the video images of river water surface were collected by UAV with video camera and RTK module，and the data was processed by video image recognition system.Finally，the flow data was successfully obtained，whose precision can meet the requirements of hydrological specifications.This non-contact flow measurement method makes the flow measurement safer，more reliable and flexible.