Abstract: The weak compressibility of water is always neglected in usual flow calculation.However, its influence upon flow calculation is obvious.To verify the influence of the compressibility on flow characteristics, the flow in a pipe is calculated by using compressible model and incompressible model, and the pressure pulsation in the pipe is obtained.Through comparing with experimental values, it is found that the pressure pulsation predicated by the cavitation model which considers the compressibility of water is closer to the experimental value than that predicted by the cavitation model without consideration of compressibility of water.