Abstract: Boundaries determination for water conservancy project management and water resources protection is one of the key tasks in the water conservancy industry in recent years. The purpose of this study is to apply 3S technology for reservoir delineation and water resources protection services. The technical method is to delineate the boundary of protection area and determine the range of aerial survey by satellite remote sensing data. Carry out unmanned aerial vehicle aerial photogrammetry to obtain DOM and DEM, and then using GIS technology to delineate boundaries for reservoir management and water resources protection. The suspected illegal areas are studied based on aerial survey results. Reservoir water quality is analyzed by remote sensing, and the distribution of water quality pollution and its relation to illegal behavior are analyzed. The information management system for water administrative law enforcement is developed to provide the services for water resources protection. Taking the Fengshuba reservoir as an example, this paper introduces the application of 3S technology in reservoir demarcation and water resources protection, UAV aerial survey, management and protection range delimitation, suspected District interpretation, inversion, and developing water quality information system; 3S technology provides the reference to the similar water conservancy project.