Most traditional assessment methods, which have complicated mathematic formulas, are difficult for calculation and application in water resources system assessment. A new approach to water resources system assessment, the set pair analysis method (SPAM), has been proposed based on the principle of set pair analysis (SPA). The basic ideals and steps of SPAM are discussed. The proposed method can take fuzzy property of threshold values for grade standards into full account and avoid determining the discrepancy uncertainty coefficient i or i1, i2, i3, … in SPA. The presented method is simple in concept, convenient to calculate and feasible for application. Two case studies of water resources assessment have been made. The results show that the proposed method is satisfactory. Most traditional assessment methods, which have complicated mathematic formulas, are difficult for calculation and application in water resources system assessment. The set pair analysis method (SPAM), has been proposed based on the principle of set The proposed method can take fuzzy property of threshold values ​​for grade standards into full account and avoid determining the discrepancy uncertainty coefficient i or i1, i2, i3, ... in SPA (SPA). The basic ideals and steps of SPAM are discussed. The presented method is simple in concept, convenient to calculate and feasible for application. Two results studies that water resources assessment have been made. The results show that the proposed method is satisfactory.