Abstract: Broad-band Acoustic Doppler Current Profiler(BBADCP) makes use of the complex correlation algorithm and the pseudo-random code technique to measure the frequency offset of the scatter of water-layers and a profiler of water current can be realized.The complex correlation algorithm makes use of the inverse tangent function,but a restricted frequency domain is obtained.Based on the previous research of time delay estimation,this paper utilizes the relationship of the result of complex correlation algorithm and the ambiguous boundary and design a more stable and more precise algorithm to solve the ambiguous problem.