Gahai Town, located in the Bayin River piedmont plain on the northeastern edge of the Qaidam Basin, is an area of the 1:50 000 map sheet that meets international standards. In accordance with the basic requirements of the Specification for Preparation of Hydrogeological Maps (1:50 000), which was developed under the guidance of China Geological Survey (CGS), and is to be issued and implemented, the hydrogeological map of Gahai Town is prepared in line with the needs of the development and construction of the town. Besides existing information and data, the hydrogeological map is based on the results and data obtained from the latest 1:50 000 hydrogeological survey in Gahai Town in 2016. It includes the results of borehole pumping tests (48 boreholes in total, including those drilled for this survey as well as already in existence, according to the data collected) and analytical results from analysis of water chemistry (61 water samples), isotope (12 isotope samples) and soluble salts in soil (55 soil samples) and the results of simultaneous measurement of groundwater level (68 simultaneous-measurement points). With the guidance of groundwater system and eco-hydrogeology theories, the dataset of the hydrogeological map is formed, based on the data processing of the groundwater system, hydrogeological structure, water-bearing rock formation and water yield properties, groundwater recharge-runoff-discharge condition, chemical characteristics of the groundwater, groundwater level depth and flow field, the relationship between groundwater and eco-vegetation, groundwater development and exploitation. Thus, it is possible to present massive information on the map by the combination of a master map with mosaic maps, clearly and hierarchically, providing groundwater data in a visualized and easy-to-use way for the development and exploitation of the local water resources, as well as for the protection of the local ecology and environment.