Abstract: The P-wave velocity V_p and the pore water pressure coefficient B in saturated soils are measured by bender element system in a GDS stress path triaxial apparatus. The evolution of P-wave signals with saturation and the effects of fluid type (tap water or de-aired water), clay content and different soil types on the relationship between V_p and B-value are considered. It is concluded that when the fluid is de-aired water or B-value reaches a certain value, the P-wave signal is composed of two parts. The first part has a smaller amplitude but a higher frequency than the second part. The first part is not affected by the effective confining pressure and the initial polarization direction of the input wave, and therefore it can be deduced as P1 wave. When the fluid is de-aired water, V_p is independent of B-value and the maximum wave velocity is constant. When the fluid is tap water, the relationship between V_p and B-value is consistent with the theoretical prediction in general when the B-value is small. When the B-value becomes large, the difference between the measured V_p and the theoretical value becomes larger. Besides, the maximum V_p in soil is greater than that in pure water, which is independent of clay content and soil type.