Wadaslintang Reservoir is located in Wadaslintang District, Wonosobo Regency. Wadaslintang Reservoir functions to irrigate an irrigation area of 6478 hectares. Operations using this reservoir need to be studied and felt less than optimal, which according to affected residents is not in accordance with the irrigation water expenditure schedule, so that farmers experience the first planting period being postponed, with this happening, farmers experience losses resulting in reduced income so there is a need for a review of reservoir water utilization using more recent data. This study begins by analyzing secondary data obtained from the Central Serayu Opak River Basin, Yogyakarta. The data is processed to get the reservoir discharge and the water requirement for irrigation water. And this study ends with a simulation of the reservoir operation pattern. From the results of this study, it is hoped that it can help provide solutions for the operating pattern of the Wadaslintang Reservoir as an optimal reservoir for irrigation needs. The results of the analysis obtained are the available flowrate for FJ Mock data generation (inflow) during 2020-2049 (Years 1 to 30), the largest available value is 25,339 m³/second and the smallest available discharge is -13,435 m³/second, the need for irrigation water is large. The maximum for the existing cropping pattern (pulses and coal) is 20,115 m³/second. And the simulation results of the Wadaslintang Reservoir operating pattern during 2020 – 2049 (Years 1 to 30) obtained reservoir reliability of 88,33 % with a failure of 11,67 % which is still below the maximum period failure of 20%. Thus, the simulation analysis of the reservoir operation pattern for the next 30 years has been in accordance with the plan and its function can still be relied upon until 2049.