It is very difficult to find an expert at the desired time and place to give guidance about irrigation scheduling or good management of water and irrigation system. In this study, this problem was tried to be solved by designing and evaluating an expert system for a modified surface irrigation system. A rule-based program named as MSISES (Modified Surface Irrigation System by Expert System) was coded and complied using C#.net programing language. The expert system was designed to support users with information about irrigation scheduling (irrigation operating time and irrigation interval) and the gated pipes as one of the surface irrigation modification tools (gates opening ratio). Two different experiments were held to evaluate the performance of the developed expert system. The first one is to evaluate the irrigation scheduling part by cultivating a field crop (Sweet maize) to make a comparison between the crop yield and water productivity after applying the program's scheduling and the farmer's scheduling. The second one is to make a comparison between the fully opened gates situation and when the resulted gates opening ratio is applied. The results indicated that an increase at crop yield and crop water productivity by 9.49% and 32.37% respectively for sweet maize using the developed expert system, and also, there was a slight variation between gates discharges after using the expert system except the last four gates discharge were different because of the superimposed pressure near the closed end.