Accurately estimation of actual crop evapotranspiration (ETa) as a parameter of irrigation scheduling is very critical for efficient use of limited irrigation water resources. The objectives of this study were to (1) build, verify and validate an expert system for managing on-farm irrigation water of some soils under Egyptian conditions, (2) study the effect of coefficient of uniformity (CU) and distribution uniformity for center pivot irrigation system, (3) study the effect of the precise estimation of daily actual crop evapotranspiration (ETa) on maximizing yield and improved water use efficiency. A rule-based program named CPISM-ES (Center Pivot Irrigation System Management- Expert System) was codes and compiled using python3.7.2 language. The program was verified using ready-to-use software programs (cropwat-8 and climwat 2) for estimating the daily reference evapotranspiration and a spreadsheet named the (FAO56Ax8.xls) introduced by FAO-56 for estimating the irrigation water management parameters. It also was validated by carrying out a field experiment at site :-El Salhyia(11.2 m above sea level, 30,35°N,30,26°E), was obtained from several different sources. The irrigation expert system aims to provide the farmers by the irrigation expertise to determine the exact water needed at exact time according to the crop requirements and the environmental factors which effect factors. The experiment included the following factors: a) obtaining climatic data from a weather station b) estimation crop evapotranspiration) coefficient of uniformity (CU) and distribution uniformity for center pivot irrigation system.  1- The estimation of actual crop evapotranspiration (ETa) using crop coefficient. 2- The seasonal cumulative ETa estimated by single-kc approach of El Salhyia (1875 m3 f.1season-1). 3- Yield: the highest of crop potatoes for El Salhyia (16.2 t.fed-1). 4- Water use efficiency: the maximum value of water use efficiency for El Salhyia (0.75 kg m-3).