Abstract: Sharp-crested weir, often installed at the inlets of small open channels, is a simple, economic and practical device for high-accurate water measurement, but current understanding of its hydraulic characteristics is not deep enough. In this study, we have investigated the hydraulic characteristics of a sharp-crested side weir using the CFD code of FlOW-3D in combination with our experimental tests, and obtained hydraulic parameters for different weir heights and different flow conditions. Water surface profiles were simulated and compared with experimental measurement. A formula for discharge was derived from the test data. The results show that the relative error between the measured and simulated values was lower than 10%, indicating a good agreement between these two methods. The fitted formula has a satisfactory accuracy of relative error range of 1.07% ~ 5.9%. Thus, the numerical results would lay a theoretical basis for design of water-measurement devices.