The Guxigou Basin is an important water replenishment unit in the upper reaches of the Minjiang River that flows into the Zipingpu Reservoir. In order to study the characteristics and influencing factors of groundwater surface water chemistry in the basin under extreme drought conditions, and to explore the suitability of groundwater resource strategic reserve site selection, 16 groundwater samples and 2 surface water samples were collected, and methods such as Gibbs plot, ion ratio, absolute principal component multiple linear regression model (APCS-MLR) were comprehensively used to analyze water chemistry and its influencing factors. The entropy weighted water quality index (EWQI) was used for groundwater quality evaluation. Analytic hierarchy process (AHP) was used to construct an evaluation system for the suitability of strategic reserve site selection for groundwater resources in river basins, and to explore the suitability of strategic reserve site selection for groundwater resources. The results show that the main cations in the groundwater surface water of the Guxigou Basin are Ca²⁺, Mg²⁺, Na⁺, K⁺, and the main anions are HCO₃^-, , Cl^-. The chemical types of groundwater are mainly HCO₃-Ca, HCO₃ -Ca·Mg, HCO₃·SO₄ -Ca; Gibbs plots, ion ratios, APCS-MLR models, and other interpreted water chemical components mainly come from water rock interactions (44.08%), industrial activities (12.17%), superimposed industrial activities in the original geological environment (11.83%), and agricultural activities superimposed domestic pollution (9.04%). Water rock interactions lead to the hydrogeochemical process of groundwater quality formation, while also being influenced by other factors such as human activities and natural environment. The EWQI evaluates the quality of groundwater as 56.25% and 18.75% for class I and class Ⅱ, 6.25% for class Ⅲ, 12.50% and 6.25% for class Ⅳ and V, respectively. The upstream of surface water is class I, while the downstream is Class Ⅳ. The overall phenomenon of gradual deterioration of water quality along the groundwater runoff pathway indicates that groundwater surface water has been affected to a certain extent by human activities. The comprehensive suitability index AI of the strategic reserve site selection of groundwater resources in the basin is between 1.0 and 9.8, and the suitable area accounts for 48.57%. The suitable area is distributed in the middle east downstream area of the basin, and the unsuitable area accounts for 51.43%. The unsuitable area is distributed in the upstream area of the basin. The research results can provide a reference for the safe development and utilization of water resources in the Guxigou basin-Zipingpu reservoir-Dujiangyan irrigation project and the layout of the strategic reserve site selection of groundwater resources under extreme conditions.