This open canal flow meter is composed of radar flow meter, radar water level meter. The flow meter is used to collect the fluid surface flow velocity, then calculate the the average flow rate across the water section by model,  combined with the water level measured by the water level meter as well as cross-section information to calculate the cross-flow cross-section area, so as to utilize the formula flow rate = average flow rate × cross-flow cross-section area correction coefficient to get the flow rate. The correction coefficient is based on the actual measurement of the environment obtained by the standard value of the calculation.