Water quality assessment of high-sulfur mining zones and the comprehensive understanding of groundwater environment are the prerequisites for the treatment and prevention of acid mining discharge. The contamination of groundwater in water quality assessment is a vague idea that stems from the inherent uncertainty of water quality classification standards and  their thresholds. To solve the problems of mismatch of evaluation criteria and absolutization of membership degree in groundwater quality evaluation by fuzzy mathematical methods, this study introduced the variable fuzzy set theory to establish a comprehensive evaluation model of groundwater quality in the high-sulfur mining area of Tongguanshan, and the ambiguity of water quality categories was dynamically identified. The results showed that the relative membership degree quantitatively characterized the subordination between the evaluation index and the evaluation standard. When the concentration of the evaluation index was within the standard range of a certain grade, the membership degrees of this grade and the grades on the adjacent sides were greater than 0. Most of groundwater quality in the study area was evaluated as grade IV and V., accounting for 89%, and the overall water quality was poor. The monitoring points M3-M7 were the position of water bursting in mine shaft with obvious characteristics of acid mining discharge, and the concentration of sulfate, iron, manganese, total dissolved solids, total hardness, and acidity exceeded the standard. Although the risk of ecological environment pollution can be reduced after the ex-situ end treatment of mine drainage, the disposal cost was high, and it is suggested that the subsequent collaborative treatment should improve the comprehensive benefits in terms of “source control” and “process blocking”.