Abstract: The core content of the new technology of detecting seepage velocity and seepage direction by sonar is introduced, including detection devices, detection principle and calculation method. It is questioned in theory and practice from four aspects: detection principle, seepage velocity calculation method, seepage direction determination and flow field distortion. After analyzing the correctness of the formula and the reliability of the data, it is considered that the principle of the sonar seepage detection lacks theoretical explanation. The formula for calculating the seepage velocity itself is not valid, and the vertical flow velocity in the hole can be obtained by using this formula, which is actually the pseudo vertical flow velocity caused by the measurement error. Regardless of whether the vertical flow is upward or downward, the time it takes for the sound waves emitted by the upper part of the probe to reach the six symmetrically distributed underwater acoustic devices in the lower plane is theoretically equal, and therefore the seepage direction cannot be obtained through the synthesis method. The provided seepage direction is actually a pseudo flow direction calculated by the exponential measurement error. The sonar method cannot obtain the seepage velocity, including horizontal and vertical flow velocities, nor can it obtain the horizontal seepage direction.