Water is one of the critical restricted factors in arid and semiarid climates. Regional water cycles are a complex eco-hydrological process, and have become a research hotspot in the context of global and increasing human activities. As one of the important services of terrestrial ecosystems, water conservation is often defined as the interception of rainwater by an ecosystem within certain spatial-temporal conditions, and attaches great importance to regional hydrological improvements, regulation of water cycle, and drinking water protection. Therefore, a clear recognition of the water conservation changes in ecological engineering areas can provide important policy references for ecological protection and restoration measures. This paper estimated the dynamic changes of water conservation service in the Beijing-Tianjin sandstorm source control project area, using the regional water balance model and GIS techniques, and analyzed the influences of topographical, climatic and vegetation factors on water conservation capacity. The results indicated that the annual rainfall increased from 224mm to 383mm in the Beijing-Tianjin sandstorm source control project area during 2000-2015, and annual evapotranspiration and surface runoff changed in the ranges of 243-355mm and 36-62mm, respectively. So the water conservation service increased in the Beijing-Tianjin sandstorm source control project area during 2000-2015, the average amount of water conservation reached 1.68 billion cubic meters, with an average water conservation capacity of 3.66mm. The water conservation capacity in the project area gradually ascended from east to west; approximately 32.45% of the project area presented high and higher levels of water conservation capacity. Compared with 2000, 41.65% of the study area showed an improvement tendency in water conservation capacity in 2015, including 22.01% of the project area, which significantly enhanced. In addition, distinct differences in water conservation among eight subzones were observed. The water conservation capacity in Desert Grassland Subzone clearly descended, while it was relatively stable in Agro-pastoral Transition Zone Grassland Subzone. Therefore, the Typical Steppes Subzone provided the largest water conservation amount of the project area, and the Yanshan Hill Mountain Water Source Protection Subzone generated the highest water conservation capacity. The dynamic changes of water conservation service could be mainly attributed to rainfall, temperature, and vegetation coverage in the project area. The improvements of vegetation coverage in Hunshandake Sandy Subzone and Horqin Sandy Subzone enhanced their water conservation capacities. In contrast, the declining rainfall restricted the water conservation capacities in Agro-pastoral Transition Zone Grassland Zone and Shanxi Northern Hill Mountain Subzone, showing climate and vegetation constraints in Desert Grassland Subzone lowered its water conservation capacity. Therefore, multiple ecological restoration strategies should be implemented for different areas in water conservation capacity.