The aquifer in the Beijing Plain is intensively used as a primary source to meet the growing needs of the various sectors (drinking, agricultural, and industrial purposes). The analysis of groundwater chemical characteristics provides much important information useful in water resources management. To characterize the groundwater chemistry, reveal its spatial and seasonal variability, and determine its quality suitability for domestic and agricultural uses, a total of 200 groundwater samples were collected in June and October 2012 from 100 exploited wells in Daxing District, Beijing, China. All of the indices (39 items) listed in the Quality Standard for Groundwater of China (QSGC) as well as eight additional common parameters were tested and analyzed for all samples, based on which research target was achieved. The seasonal effect on the groundwater chemistry and quality was very slight, whereas the spatial changes were very obvious. The aquifer is mainly dominated by HCO3-Ca·Mg-type water. Of the 39 quality indices listed in QSGC, 28 indices of all of the samples for the 2 months can be classified into the excellent level, whereas the remaining 11 indices can be classified into different levels with the total hardness, NO3, NO2, and Fe being the worst, mainly distributed in the residential and industrial land. According to the general quality index, the groundwater can be classified from good to a relatively poor level, mainly from southeast to northwest. Furthermore, the relatively poor-level area in the northwest expands to the southeast more than in the past years, to which people should pay attention because this reverse spatial distribution relative to the natural law indicates an obvious, anthropogenic impact on the groundwater. In addition, the groundwater in this area is generally very suitable for irrigation year-round. Nevertheless, we recommend performing agricultural water-saving measures for the sustainable development of water and urbanization, groundwater recovery, and ecological safety.