Abstract: Acoustic Doppler velocimetric equipment often uses complex covariance algorithm to measure Doppler frequency shift. When the echo amplitude is limited, the frequency shift measurement bias occurs, which leads to velocimetric bias. Based on the complex covariance algorithm, the causes of Doppler velocimetric bias due to echo amplitude limiting are analyzed, and the rule that the frequency shift measurement bias for the amplitude limited echo signal changes with the real frequency shift is revealed, which appears as a change in a sinusoidal oscillation. The simulations of echo amplitude limiting for narrowband and wideband transmitting signals are performed respectively. By the acoustic Doppler velocimetric simulator and the sea trial, the amplitude limited and unlimited echo data of the acoustic Doppler velocimetric equipment are acquired, and the simulation and test results are consistent with the theoretical analysis.