Spillways are among the most important hydraulic structures and have the greatest impact on flood control systems. Circular spillways are often used in narrow valleys and with earth dams. Previous studies have focused on this type of spillway due to its sensitivity and importance. where it is proven One of the most crucial elements affecting a circular spillway''s performance is its discharge coefficient. This coefficient gauges how effectively a spillway can move water over a range of dimensions. In this research, we established a physical model in the Irrigation and Hydraulics Laboratory, Department of Civil Engineering, Faculty of Engineering, Al-Azhar University, Cairo, Twenty laboratory experiments were conducted and their measurements were taken and compared with the results obtained from the numerical model that was generated by Flow 3D software. The purpose of the comparison is to validate the numerical model, which can be used to predict the hydraulic characteristics of circular spillways in the future based on the results, it became clear that the numerical model is highly efficient, with an average error rate of no more than 10% in calculating the water height above the spillway crest and no more than 12% in measuring the discharge coefficient. so, the numerical simulation in the flow 3D software is capable of simulating flow over a circular spillway.