: The common gate and weir systems are being used for measuring flow discharge in open channels. But in some cases, passing water with flouted material or sediment can cause some disruptive effects on their performance and also it can increase the measuring error. In order to solve this problem, weir and gates can be combined and create an intensive hydraulic system known as gate-weir, by this way it will let the sediment to traort under the gate and also let the floated particles pass through the above of weir. Generally the structures should be modeled before the fabrication process, because it can prevent from excessive and sometimes unnecessary costs. But there is a problem that sometimes the behavior of the physical model differs from the behavior of original scale, and therefore the extension of the obtained information from the simulation model does not cover all aspects of the original system. Moreover, there are many serious problems in measuring process and also measuring tools. Therefore, software has been developed, that they are using the mathematical models and theoretical predictions, to minimize the differences between the model and prototype studies. In this study, numerical simulation of flow in the combined model weir - gate has been accomplished by using the CFX software. The discharge that has been separated by using software were compared with provided equations by the Swamee (1988) and Kindzvatr-Carter (1957) for the weir and Swamee (1992), Benjamin and Beirami for the gate. All equations presented acceptable magnitude ??for the amount of calculated discharge in comparison with the numerical model. All presented equations for weirs and gate were combined and flow rate passing through a combined weir and gate structures were calculated and compared with laboratory discharge values. Between all presented combination equations, the compound equation containing Kindzvatr - Carter (1957) for the weir and Benjamin for the gate has the minimum error. After making the comparison between the experimental values with results of presented equations, the C coefficient was calculated for the compound equations and the results were assessed with different statistic indices. All presented equations for the combination weir and gate had the maximum ±3/6 error. Using the Kindzvatr- Carter for calculating the discharge in the weir and also using the Benjamin equation for the gate had a minimum range of error in calculating the flow discharge in the weir gate as a combination of structures. The magnitude of the error for all tested discharge that they passed through the combination of structures was in the range of ±1/7. On the assessment of the gate’s submergence effect on flow rate passing through the compound structures some results were observed. By this way with increasing the submergence, flow rate passing through the gate does not change until the weir submerged and also when the weir being submerged the flow rate will decreases. Key words : combined weir and gate, sharp edges weir, sluice gate, combined Discharge, Computational fluid dynamic