The natural conditions in the arid area of northwest China are very bad, precipitation is low, evaporation is intense, and water resources are scarce. In the meantime, natural lakes and wetlands, natural vegetation oases and soil salinization are strongly dependent on the ecological water level of groundwater. Therefore, it is an important challenge to construct the evaluation index system of groundwater ecological function in northwest arid area. Based on the study of the relationship between different types of ecological conditions and groundwater table depth in arid area, the evaluation index system of groundwater ecological function in arid area of northwest is constructed using the shallow groundwater as the core factor. It is composed of 3 attribute indexes that include the maintenance of natural wetland landscape by groundwater, the maintenance of natural vegetation oases, and the maintenance of farmland land quality. The application results in the middle and lower reaches of the Shiyang River basin show that the index system may offer reference for the evaluation of groundwater function in the arid and semi- arid areas of northwest China, and it also indicates that the ecological function of groundwater in the middle and lower reaches of the Shiyang River Basin is fragile. The weak ecological function accounts for 87. 86% of the total area of the demonstration application area, while the strong and strong ecological function of groundwater accounts for only 5. 07%. Therefore, it is urgent to improve the ability of groundwater ecological function protection in arid area of northwest China.