Abstract: A numerical hybrid normal modes/Kirchhoff approximation method is brought forward to predict the acoustic scattering pressure for large complex target in shallow water waveguide. This study uses the Kirchhoff approximation approach and normal modes model to calculate target scattering function and acoustic propagation respectively. The present numerical method is validated by analytical benchmark solution for rigid sphere scattering in an ideal shallow water waveguide and it has been proved to be an accurate engineering prediction method. Interference structure of scattering pressure for a rigid sphere in Pekeris shallow water waveguide in the range-frequency domain and the depthfrequency domain are numerical analyzed and compared with free space situation. Echo in the time domain is obtained by FFT and then the effects of target posture and sound velocity profile on echo from Benchmark submarine target are discussed.