Abstract: In view of the calculation time-consuming of multibeam constant gradient sound ray tracking and the reduction of the calculation accuracy due to the simplified sound velocity profile, based on the analysis of the multibeam constant gradient sound ray tracking theory, a method based on time decomposition is proposed. The tracking method is to decompose the propagation time of the beam in the layer into a fixed term which is independent of the beam incidence angle and related variable terms. The fixed term only needs to be calculated once for each sound velocity profile, and the first order approximation of variable term is obtained by using McLaughlin ’s expansion. The order approximation simplifies the calculation of the propagation time and the horizontal displacement in the layer, and at the same time the simplified sound velocity profile is only applied to the variable term to reduce the calculation error of the remaining time. Experimental results show that when the beam angle and layer spacing or sound velocity difference between upper and lower layer is less than 50° and 50 m or 20 m/s respectively, the approximate model has the same accuracy as the constant gradient algorithm. The time decomposition model can significantly improve the accuracy of sound ray tracking when the layer spacing of the sound velocity profile increases.