Fracturing technology is one of the most efficient ways to productivity evaluation, and the key of fracturing technology is how to describe rock mechanical behaviors to which S-wave slowness is an important parameter. According to the complexities of low porosity and low permeability of Pucheng oilfield, we designed and obtained the experimental scheme for measuring the velocities of P-wave and S-wave. The samples are focus on dry sample and rock with water saturation 100%, 80%, 60% and 40% respectively, under two conditions at normal temperature with 5MPa and with formation pressure at 90°C. By conducting triaxial test, the velocities of P-wave and S-wave under different temperatures and different pressures were obtained. On the analysis of 26 groups of data, the results showed that on the formation condition, S-wave slowness value varied linearly with water saturation, and S-wave slowness was also linear to P-wave slowness at different water saturation. Oil-bearing layer and water layer models were created separately, to compute S-wave through P-wave based on linear interpolation. We validated the new approach with an example from real array acoustic log data of Pushen 18 well. The results demonstrated the advantages of this method over empirical equation proposed by Entwisle’s and Dreiser Company. The relative error from them compared with log data are more than 10% whereas that of our method is 4.2%.