Water conservation is an essential service for terrestrial ecosystem, which plays an important role in water supply, runoff regulation, and water mitigation. However, current researches on water conservation in river headwater areas are rarely reported, especially the study of spatiotemporal evolution of water conservation over a long period of time. This study adopts the WEP-L distributed hydrological model and the water balance equation to analyze the water conservation in the headwater area of the Ganjiang River and its influencing factors during 1957-2018. The results show that the annual mean water conservation is 552.3 mm in the headwater area of the Ganjiang River over the study period, with a growth rate of 0.85 mm/a. The annual water conservation ranges from 44.2 to 1 178.6 mm, characterized by a greater distribution in the north and south and a smaller distribution in the west. The variation trend of water conservation in the study area ranges from -1.99 to 5.45 mm/a, which is high in the north and low in the south. The coefficient of variation changes in the range of 0.27-2.91, with 82.68% of the area lower than 0.55, indicating relatively small fluctuations. Precipitation is the main factor influencing the spatiotemporal variations of water conservation. This study can provide a technical support for water resources and ecological protection.