Abstract: With the thermal phase change model in computational fluid dynamics code ANSYS CFX,the mixing condensation process of gaseous oxygen and liquid oxygen in pump pipeline was numerically simulated.Moreover,the dispersion equation of two-phase pressure wave propagation was derived via the ensemble average two-fluid model,and was used to predict the pressure wave propagation speed in pump pipeline.The results indicate that,with the increase of void fraction,the two-phase pressure wave propagation speed in pump pipeline first decreases and then slightly increases in slug flow,and the propagation speed increases as angular frequency enlarges.When liquid oxygen mass flow rate increases or inlet gaseous oxygen temperature decreases,the condensation effect of gaseous oxygen in pump pipeline enhances and the average void faction along the flow direction decreases,thus producing large pressure wave propagation speed.