Groundwater environmental investigation and assessment serve as the foundation for groundwater pollution prevention and prediction. In this chapter, the TOPSIS method was selected as the fundamental evaluation approach. Building upon this, the information entropy theory was employed to determine the weights of various indicators, thereby formulating the entropy-weighted TOPSIS method to achieve a more comprehensive and accurate assessment of water quality. This integrated approach enhances the robustness and reliability of the evaluation, ensuring that the results are both scientifically sound and practically applicable. In addition to groundwater quality assessment using the entropy-weighted TOPSIS method, this chapter also summarized the main environmental issues related to groundwater in the Weining Plain, and discussed the evolution of groundwater system under human activities in this plain.