Abstract: In order to improve the predictive accuracy of 1D water hammer model for transient flow in pressurized pipelines, an additional transient friction term was introduced into the traditional 1D steady friction model and an improved unsteady friction model was developed. Using these two models, the pressure transient characteristics of a reservoir-pipeline-valve system were numerically simulated for three different steady-state initial flow velocity conditions. The predictive accuracy of the two models was compared. The results indicate that both the steady friction model and the improved unsteady friction model closely approximate the pressure variations in the first period of the pressure wave, in accordance with experimental values. However, after the first pressure wave period, the errors in predicting pressure peak values for low initial velocity conditions are 10.3% and 4.7% for the steady and unsteady friction models respectively. The improved unsteady friction model shows significantly enhanced predictive accuracy. Research into pressure wave propagation characteristics reveals distinct differences in wave propagation and reflection behavior at different locations in the system. During one water hammer period, pressure waves experience complete negative reflection at the reservoir due to pressure difference effects, while at the valve, the waves only change direction due to negligible velocity change in the micro-fluid section. These findings contribute valuable insights into the safe and stable operation as well as optimization design of pressurized pipelines.