Abstract: The measurement of the river discharge by acoustic Doppler current profiler (ADCP) depends on the accurate depth measurement. In the case of wrong depth measurement, the reasonable value should be used to interpolate the depth for the wrong frame to increase the calculation accuracy. Based on the analysis of the theoretical standard deviation of depth measurement by ADCP in the slope river bottom environment, a new method using the ratio of four-beam depth standard deviation to average value for depth filtering is proposed in this paper, and the preserved depth measurement values are used for fitting and prediction calculation, by which, the accuracy of depth interpolation for the invalid frame is improved. Compared with the previous depth filtering methods, this method further increases the filtering ability of depth out-liers and improves the calculation accuracy of discharge.