Abstract: In order to explore the water environment quality and pollution characteristics of lakes with different total dissolved solids (TDS) concentrations in the Inner Mongolia section of the Yellow River Basin, ninety-seven typical lakes in the Inner Mongolia section of the Yellow River Basin were studiedd and classified into five categories from L1 to L5 according to TDS gradient: L1 for brine lake, L2 for salt lake, L3 for brackish lake, L4 for slightly brackish lake, L5 for fresh water lake. Based on 11 water quality indicators, the water quality index method (WQI), hierarchical cluster analysis (HCA), and positive matrix factorization (PMF) model were used to categorize and explore the characteristics of the water quality of the lakes in the five categories and their pollutant sources. The results showed that most of the lakes in the Inner Mongolia section of the Yellow River Basin had poor (34.02%) and moderate (55.68%) water quality, and only five lakes had good water quality. The cluster analysis showed that it was scientifically and practically feasible to categorize lakes based on the TDS to explore the water environment quality. Using the PMF model, five pollution sources for that lake were identified: COD was mainly affected by livestock and poultry breeding pollution; TN was mainly affected by surface runoff pollution; TP was mainly affected by agricultural cultivation pollution; NH₃-N was mainly affected by rural life pollution; DO was mainly affected by natural sources. Surface runoff-agriculture composite pollution was dominant in lakes L1 and L5 (28.72% in L1 and 38.23% in L5), rural life pollution was dominant in lakes L2 (accounting for 31.81%), and the highest contribution of natural sources and livestock and poultry pollution was found in L3 and L4, which were 30.35% and 41.73%, respectively. These findings quantify the contribution rate of pollution sources in lakes with different gradient TDS concentrations, which provides a basis for differentiated management of lakes in the Inner Mongolia section of the Yellow River Basin.