Abstract: OBS has been rapidly developed and widely used in China in the past years based on self-made instruments and own working teams under various sea conditions. It is used in the study of crustal structures and for earthquake monitoring in the ocean. In this paper, we put our focus on OBS data processing methods for speed imaging. The ratios of P-wave and S-wave of various lithology provided by previous studies are discussed. Data processing usually includes demultiple, time cutting, time and position correction, horizontal component rotation (mainly for shear wave processing) and others to enhance the signal-to-noise ratio and to improve the resolution. Velocity model is built by Rayinvr, fitting the theoretical and observational travel time of reflection and refraction waves from different interface. Vp/Vs is closely related to lithology, pore filling material and porosity. Uncompacted deposits generally have a higher wave velocity ratio. Vp/Vs of the rock filled with fluids is higher than the one filled with gas due to a lower shear wave.