In order to study the impact of leakage on the change of hydraulic factors in water supply pipelines, the internal flow and flow field change process of a water supply pipeline with or without leakage point and different leakage point sizes were simulated based on computational fluid dynamics (CFD) method. According to the simulation results of pipeline 1, when t=4 s, the flow velocity near the proposed leakage point of the non-leakage pipeline was 0.16 m/s, and the pressure was 0.015 kPa; whereas the peak velocity of the pipeline with leakage was 0.32 m/s, and the peak pressure was 0.068 kPa. The overall results of the pipeline show that when there is no leakage in the pipeline, the fluctuation of pressure and flow velocity in the pipeline section near the proposed leakage point is small. Due to the leakage, the pressure and flow velocity in the pipeline section near the leakage point reach the peak value, and the pressure and flow velocity in the downstream pipeline section of the leakage point are significantly lower than those of the non-leakage pipeline. Under different simulation conditions, the variation trends of flow velocity and pressure in the pipeline with leakage are consistent, but the pressure changes more sharply than the flow velocity. In addition, the change of leakage point size is inversely proportional to the change of flow velocity and pressure in the pipeline. This study can provide some referential value for the formulation of water supply pipeline leakage monitoring scheme and the optimization of monitoring equipment layout.