This study is to develop a Priority Decision System for Redevelopment (PDSR) which is able to decide the priority for redevelopment of agricultural reservoirs. The major scopes of this research are to make the related GIS data like hydrologic unit map and other thematic maps to determine the suggested priority index (PI), and to develop the PDSR handling the GIS data and calculating weighing factors for the PI. In order to make the weighing factor decision module, the AHP technique was adopted. The result of the weighing factor calculation was showed PC (Possibility Criteria) and RC (Restriction Criteria) were 76% and 24% respectively. Which means that most of the specialist selected PC category prior to RC because of whom to mostly of major technique. So, in order to make more objective result, the selection of specialists is important like environmental activists or local residents and so on. The product from this research can provide more scientific support to decide the priority decision.