To address the severe water inflow issue in the underground workings of the Mingniwan Phosphate Mine in Guizhou, after confirming substantial water loss from the surface river, water samples were collected from six underground water inflow points, the dolomite aquifer, and the Yangshui River for hydrochemical analysis. Six hydrochemical components, Ca²⁺, Mg²⁺, Na⁺+K⁺, , Cl^- and , were selected as discrimination indicators. The Piper trilinear diagram combined with Grey Relational Analysis (GRA) was applied to identify the sources of underground water inflow. The results show that the hydrochemical types of water samples from the Yangshui River, the 368 m grit chamber, the 490 m water sump, the 440 m goaf, the 524 m water sump, and the 520 m drift are all type, while those from the 650 m main slope surface and the dolomite aquifer are type. The water inflow source in the 440 m goaf is most likely from the Yangshui River, with the highest correlation degree of 0.94. The 650 m main slope surface shows the lowest correlation with the Yangshui River, but its correlation degree with the dolomite aquifer reaches 0.86, indicating a strong correlation, suggesting that the dolomite aquifer is a highly probable water inflow source. The Piper-GRA combined analysis method provides an effective technical solution for identifying water inflow sources and can serve as a scientific basis for subsequent formulation of water prevention and control measures.