The LS25-1 deep-water gas field, with its long-distance pipeline and steep climbing sections, presents challenges in predicting the arrival time of the water phase of multiphase fluid, posing risks to pipeline flow assurance. Based on the multiphase flow equation, LedaFlow software was used to study the water phase movement in the initial startup stage of the deep-water gas field and to analyze the influence of water cut, oil flow rate, gas flow rate and oil-water interface friction coefficient. The results indicate that during the initial start-up stage, water can separate and accumulate in the uphill regions, creating pools of water that are essentially stagnant. In regions with larger pipeline slopes, the water phase experiences violent fluctuations. A higher water content in the fluid leads to shorter accumulation times in uphill regions; an increase in gas flow rate can diminish water phase stagnation and expedite water movement in these areas; Variations in oil volume have a relatively low impact on the movement of the water phase. Oil-water interface friction coefficient has a direct impact on water phase accumulation in the uphill section and precise adjustments to this coefficient are of significant guiding importance for actual pipeline operations. This research result can provide a reference for the development of deep-water gas fields.