Abstract: In view of the high cost of ocean sound velocity profile measurement and the difficulty of long-term observation, the method using the sound signal propagation time delay between a fixed underwater reference point and a known position on the water surface to invert the ocean sound velocity profile is studied. A sound velocity profile inversion method based on the isosonic layered model is proposed. The seawater is layered, the sound signal propagation process is modeled, and the non-linear equations for inverting the sound velocity are derived. Then the Newton iteration method is used to solve the non-linear equations. Through simulation and sea trial data processing, it is shown that for different numbers of layers, the error between the inverted sound velocities and the actual sound velocities become smaller with the increase of the number of layers. The minimum error is about 0.80 m·s^-1, which verifies the effectiveness and accuracy of the inversion method.