Sharp-Crested weirs as measuring devices are widely used in hydraulic laboratories. They are also useful as water surface or flow controlling structures at many irrigation networks. In this paper, an attempt was made to simulate flow over rectangular and triangular sharp-crested weirs with flow under slide gates. Based on the continuity equation, an empirical equation for the coefficient of contraction, and also discharge coefficient of the rectangular slide gates, flow discharge over rectangular and triangular sharp-crested weirs are proposed. A comparison was made between the proposed theory and few experiments conducted at Isfahan University of Technology. The proposed empirical equation was also compared with those of other researchers. The results showed that the proposed method could predict flow discharge over the weirs with high accuracy.