Groundwater utilization and protection are crucial for sustainable urban development. This is especially true for Beijing, where groundwater is an important source for urban water supply. In this study, statistical methods, including descriptive statistics, correlation analysis, principal component analysis, and Piper-Tri-linear diagram, were used in analyzing the temporal and spatial variations of the hydrochemical characteristics of groundwater based on monitored data from the southern plain of Beijing, China. Results indicated consistent changes of groundwater’s hydrochemical characteristics in different aquifers in the study area. The percentage of HCO₃^- in total anion increased significantly in the groundwater, and hydrochemical water type evolved gradually from Ca-Mg-Cl-SO₄ based to Ca-Mg-HCO₃ based from period 2005-2007 to period 2013-2015. In shallow groundwater, the concentration of Na⁺, Ca²⁺, SO₄^2-, HCO₃^-, and total dissolved solids (TDS) increased from period 2005-2007 to period 2013-2015, and the greatest change came from HCO₃^-, rising from 428.93 to 528.96 mgL^-1. The changes of main ionic concentrations in the deep groundwater were consistent with those in the shallow groundwater for both periods. However, the variations in deep groundwater were less than those in shallow groundwater. The temporal and spatial variations of hydrochemical characteristics reflect the groundwater quality in the study area. This study could facilitate decision-making process on the protection of groundwater resources to ensure its sustainable utilization.