The level of water quality assessment is significant for preventing water pollution; many factors influence its assessment. At first, the TOPSIS-GRA model is introduced; the comprehensive closeness degree of different samples is calculated; finally, the quality level of groundwater is determined based on the comprehensive closeness degree. The conclusions are drawn that results obtained using the suggested method are consistent with the actual investigation for four samples. The accuracy reaches 100%, which is higher than the results from the traditional Matter-Element Extension Model (80%), and estimating the quality level of groundwater using the suggested model is feasible. Since this evaluation method fully utilizes sample data information and combines the advantages of gray correlation analysis and the TOPSIS evaluation model, the evaluation results are more accurate and reasonable than those of a single evaluation method. Therefore, it provides a new method and thoughts to assess the quality level of groundwater in the future.