Abstract: Quantitative evaluation of urban water resources security has great significance for making reasonable development strategy of urban water resources, promoting sustainable utilization of water resources, realizing sustainable development of social economy. An index system of water resources security evaluation is established, including water resources quantity security, water environment security and social and economic security subsystems. Combined weights of indexes are determined using analytic hierarchy process (AHP) and entropy value method. The model of urban water resources security evaluation is constructed based on the set pair analysis (SPA) and the variable fuzzy sets (VFS). Water resources security of Guangzhou and its main obstacle factors are analyzed from 2004 to 2014. The result shows that there is a tendency of gradual improvement in water resources security conditions in Guangzhou, upgrading from "less safety" to "critical safety" level. The primary factor affecting water resources security is water resources quantity security. Main obstacles hindering water resources security level of Guangzhou are water resources quantity per capita, water resources quantity per unit area, and guest water proportion. Evaluation model is more objective in reflecting the temporal evolution characteristics of urban water resources security and main restrictive factors. The result is in line with reality. The proposed model provides a practical and intuitive way for evaluating urban water resources security.