A kind of three-dimensional（3-D） sound ray tracing algorithm in heterogeneous media is studied. This algorithm includes two steps： the first step computes the wavefront traveltimes forward; the second step traces the sound rays backward. In the first step, the computation of wavefront traveltimes at discrete grid points from the sound source, was found on Eikonal equation solutions and carried out by GMM （Group marching method） wavefront marching method based on level set. In the second step, sound ray tracing was proceeded gradually from the receiver to each cell towards the sound source, with wavefront traveltimes computed in the first step. Time values on arbitrary positions in each cuboid cell can be expressed by linear interpolation of wavefront traveltimes at the same cell＇s grid points. Thus, an algorithm of 3-D sound ray tracing in heterogeneous media is put forward. The simulation results indicate that this method can improve both the accuracy and the efficiency of 3-D sound ray tracing greatly.
