Optimal water management is to efficiently and equally supply an appropriate amount of water by using irrigation facilities. Therefore, it is necessaryto evaluate water supply capacity through distribution simulation between the designed distribution rate and re-distributed rate according to the changedfarming conditions. In this study, we recalculated the agricultural water supply amount of Geumcheon main canal, which beneficiary area was reduceddue to the development of Gwangju-Jeonnam innovation city, and we constructed a canal network using the SWMM model to simulate the change insupply rate of each main canal according to the re-distributed rate. Even though the supply amount of the Geumcheon main canal was reduced from1.20 m3/s to 0.90 m3/s, it showed a similar supply rate to the current, and the reduced quantity could be supplied to the rest of the main canal. Asa result, the arrival time at the ends of all main canal, except for the Geumcheon main canal, decreased from 1 to 3 hours, and the supply rate increasedfrom 4 to 17.0% at the main canal located at the end of the beneficiary area of Naju reservoir.