Abstract: Normal modes interference can result in longitudinal-correlation decreasing of the acoustical field in ocean waveguides, so it will lead to the gain decreasing of wide-aperture array. Based on the waveguide invariance, the linear phase relationship between the frequency response functions of the two points with certain longitudinal separation in a channel is put forward. With the linear phase relationship, a frequency-shift compensation method is proposed, which can be used to improve the longitudinal correlations of acoustical field.Results from a shallow-water acoustical experiment show that the spatial correlations of the signals received by the horizontal array can be improved significantly by the frequency-shift compensation method.