Abstract: The underwater system designed for detecting objects buried in sea-bottom often operates at large stand-off distances and insonifies the bottom with subcritical grazing angles. It is impossible to predict the performance with ray models. Combining the wavenumber integration model and virtual source approach,this paper develops a hybrid model,which can calculate the 3D scattering field accurately for buried objects with different shapes,buried status and arbitrary beam-pattern of sources. With the scatt-ering model,the effective target strength and the signal-to-reverberation ratio are calculated for different values of frequency,grazing angle and burial depth. In addition,a bistatic system frame based on time reversal focusing is presented and validated in principle with sound field analysis,which provides a poss-ibility of detecting the buried objects at large distance.