Sinai is a rigid region and one of the most important strategic areas in Egypt for its historical importance, its location, Its touristic importance, and its natural resources. the lack of water sources in Sinai is the most important reason for the lack of development in it. so the study aims to estimate the runoff in wadi Tayyibah which located in south Sinai to benefit from it in different uses and avoid the hazards which occurred due to the floods through design protection structures that depend on the amount of runoff. The present study aims to evaluate the runoff, morphometric properties and delineate the watersheds in Wadi Tayyibah relying on The Soil Conservation Service Curve Number (SCS-CN) method besides Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) model which is a hydrological model that be used to estimate the runoff and produce the hydrographs for storms with different return period5,10,25,50and100 years, that model also be used in watershed delineation for the study area. The Arc-GIS is used in hydrological and topographical analysis and used to represent the characteristics of the case study in maps. The rainfall data which be used was for Abou Redus rainfall station in monthly data from1976 year to2018 year. The frequency analysis has been done using Microsoft Excel which produces storms with depths20.6,29.2,40.7,49.3,58mm of return periods5,10,25,50and100years, respectively. The runoff as a volume 0.18, 0.911, 2.53,3.89 and 5.89 Mm3 and as depth 0.5, 2.56, 7.10, 10.93 and16.54 mm of return periods respectively