In order to solve the problem that it is impossible to evaluate the results of video flow measurement in the actual hydrological measurement, a specific test device is needed to test the accuracy of various flow measurement methods. This paper designs a non-contact flow velocity measurement result inspection device for open scene by using programmable logic controller (PLC). Through this device, the measurement results of various video flow measurement methods are inspected, thus providing a new calibration method for video measurement. Firstly, this paper designs a non-contact flow velocity measurement device for open scenes; secondly, high frame cameras are used to capture experimental videos with different frame rates; finally, three mainstream video flow measurement algorithms are used to measure experimental video flow velocity, and the measurement results are compared with real data, the results show that the error of the three algorithms is more than 20%. The experimental results show that the mainstream video current measurement methods have great errors in low velocity.