In order to simulate the target echoes scattered from submerged underwater objects, Kirchhoff approximation is widely used for high frequency region. Since Kirchhoff integration is based on integrating the contributions from discretized boundary elements, the computation can be time-consuming especially for broadband pulses. In this thesis, a numerically efficient method for generating the scattered signal in time domain based on convolution is proposed and tested. It it shown that the computational time can be reduced by an order of 10~100 in typical cases.