Abstract: A sound ray tracing algorithm is presented, which helps to rapidly find the sound ray trajectories in three-dimensional (3-D) space. At each step of ray tracing, a small regular tetrahedron is made in front of a ray, so that the sound speed field inside may be approximately regarded as linear. Since a ray trajectory in the linear sound speed field is always in a plane, it may be obtained by the two-dimensional sound ray tracing method by deploied triangle. The theoretical derivation is given and a numerical model is discussed which shows that the algorithm is fast and precise. It is more concise and reliable than the traditional 3-D algorithms, and may be used to avoid the damage to the precision by the acoustic refraction in the 3-D ultrasound computerized tomography.