The problem of high resolution echoes time delay estimation for large time-bandwidth preduct LHM signals is investigated. A novel algorithm based on FFT for LFM signals enhancement used for preprocessing to raise the effective signal-to-noise ratio （SNR） is presented. In Order to overcome the redution difficulty in the case that echoes are highly correlated or coherent

ROOT-WSF algorithm is applied by use of inverse filtering in signal bandwidth. Finally

simulation results are included to demonstrate the improved perfornmnce achieved by the proposed method.