Abstract: Identifying the water inrush source accurately is a fundamental work and crucial for safe mining in coal mines. This study focuses on a coal mine in Gansu Province based on a comprehensive method of Piper trilinear diagram, hierarchical clustering and gray rational analysis. The water chemical types of underground drainage, fault fissure water and roof sandstone fissure water in the working face are all SO₄-K·Na type and the water chemical types of ground is SO₄·HCO₃-Ca type. In the Piper trilinear diagram, the underground drainage water sample is far from other water sample points, indicating the underground drainage water may be mixed from multiple sources. Hierarchical clustering analysis shows that the underground drainage water is relatively close to the water chemistry of roof sandstone fissure water and fault fissure water. Finally, the gray rational analysis indicates that underground drainage water is better correlative with roof fissure water and fault fissure water. According to the aforementioned comprehensive method, the underground drainage water is mainly derived from roof sandstone water and fault fissure water, yet has little relations with surface water. It is speculated that it may be the roof water supply caused by strata disturbance during the mining process, as well as the pore water supply through the water conducting fracture zone. Therefore, the research and exploration of the roof aquifer and water conducting fracture zone will be of great importance in the future work of water prevention and control in the coal mine.