Abstract: A moving synthetic aperture processing with high resolution spectral analysis method was proposed to estimate the mode wave-number of acoustics in shallow water waveguide,and to overcome the problem of short aperture. First,large aperture synthetic array is created by the moving of short horizontal array,then a MUSIC processing is applied to the estimation of normal mode wave-number.The simulation and sea trial results indicate that the problem of short aperture can be resolved by using of synthetic aperture processing,as well as the accuracy of estimation in normal mode wave-number can be improved by varying the array depth when it is being towed away from the source.