[Objectives] The unique Zhangshiyan landform of the Taihang Mountains is characterized by distinct horizontally layered hydrogeological formations, consisting of upper carbonate rocks, middle‑upper claystone, middle‑lower quartz sandstone, and basal metamorphic gneiss. Regional tectonism has developed abundant wide‑opening fractures within the quartz sandstone layer, forming complex and heterogeneous groundwater seepage networks. The underground cavern group of a pumped‑storage power station is constructed within quartz sandstone strata below the river erosion base level, inducing severe water inrush during excavation. The steady inrush discharge ranges from 20 000 to 30 000 m³/d, with a peak value of 55 000 m³/d. The alternating aquifer‑aquiclude structure leads to complicated mixed recharge processes, making source identification extremely difficult. This study aims to clarify the spatial differentiation characteristics, recharge mechanisms, and quantitative contribution rates of multiple water sources, so as to provide a scientific basis for water inrush risk prevention and optimal drainage design for underground projects in layered landform areas. [Methods] Based on detailed field hydrogeological surveys and engineering layout characteristics, a total of 16 water samples were systematically collected from surface river water, karst groundwater, sandstone fracture groundwater, and cavern water inrush points. A three‑step comprehensive identification method was established in this research. Firstly, Piper diagrams and ion ratio analyses were adopted to qualitatively classify hydrochemical types and preliminarily distinguish different groundwater end‑members. Secondly, principal component analysis and cluster analysis were applied to screen independent and dominant water source components and eliminate overlapping hydrochemical information. Finally, a geometric distance model between water inrush points and typical end‑members was constructed to quantitatively calculate the mixing proportion of each water source and reveal the spatial variation law of recharge sources at different burial depths. [Results] The underground water inrush is jointly controlled by three typical water source end‑members, namely in‑situ sandstone fracture water, karst fracture water, and river surface water. Significant spatial differences in recharge patterns are dominated by cavern burial depth and relative base‑level elevation. Shallow caverns buried approximately 100 m above the erosion base level are entirely recharged by single‑source karst fracture water infiltration. In comparison, deep caverns buried 250-300 m below the base level present obvious multi‑source mixed recharge characteristics. The contribution proportion of in‑situ sandstone fracture water ranges from 24% to 36%, river surface water accounts for 29% to 54%, and karst fracture water contributes 22% to 35%. Surface water infiltration serves as the dominant recharge source for deep cavern water inrush, while endogenous fracture water and upper karst water act as auxiliary recharge sources.[Conclusions] The river erosion base level and layered stratigraphic structure are the key controlling factors for the differential water inrush mechanism in Zhangshiyan landform. Shallow caverns exhibit single karst water recharge, whereas deep caverns are dominated by mixed multi‑source recharge. The proposed “hydrochemical diagramming + multivariate statistics + end‑member quantification” integrated system can effectively achieve qualitative discrimination and quantitative inversion of complex water inrush sources. The research findings reveal the layered groundwater recharge and seepage mechanism, providing reliable technical support for water hazard control in pumped‑storage underground caverns. This method can be popularized and applied to similar underground engineering water source identification in mountainous layered stratigraphic regions.