In this book, the time reversal focusing based on finite difference time domain (FDTD) method to localize source by using MATLAB GUI. There are three analyses of free space model, waveguide model and user define model for source location in a perfectly matched layer boundary. The simulation results are evaluated to localize the source by using FDTD method in this book. This book is appropriate for analyzing the time reversal mirror implementation. We have shown the energy spectrum for propagation of acoustics wave in a room to focus by using array of transducers and source. In these plots we first transmit the signals from source to the array of transducers and then the signals can be retransmitted back from array of transducers to the source by using time reverse algorithm.The application areas of this work are mentioned in this work.