A propagation path of sound wave in shallow water may contain some obstacles, such as sunken ship and structure. In order to analyze the waves reflected from the object in the sound field, we have to analyze the reflected pulse wave in time domain. The solution of the time dependent wave equation can be obtained via a Fourier transform of the frequency domain solution. However, it is difficult to obtain a solution in frequency domain for the sound field including complicated objects. We analyze the reflected and diffracted wave from an object using the FDTD method directly analyzing in time domain. Furthermore, time reversal processing to the reflected and diffracted wave is carried out, and time reversed wave is reradiated from the time reversal array (TRA). And the convergence characteristic of the wave carried out time reversal is investigated