Broad-crested weirs are structures that are commonly used and exploited in open channels. The purpose of using these weirs, is to measure water discharge and also to control the flow through open channels. trapezoidal broad-crested weirs is one of a kind of broad-crested weirs. In this study, eight experiments were conducted at the Hydraulic Laboratory of Isfahan University of Technology. Experimental results such as water surface profiles and velocity profiles for four discharge on U 30 -c-D 45 and U 45 -c-D 30 trapezoidal broad-crested weirs were obtained. Then, using the FLOW-3D software version 10.0.1.7 and utilizing the RNG K-e turbulence model, the flow was simulated for eight existing experiments, and numerical results and experimental results were compared. The quantitative accuracy of the numerical results of this research was investigated by a variety of statistical indices including NRMSE, agreement index (d), and also the coefficient of Determination (R 2 ). In the water surface profiles results, the average of the NRMSE, d and R2 indices for the eight existing experiments was 2.43, 0.9995, and 0.9988, respectively. In the velocity profile results, the average of the NRMSE, d and R2 indices for the eight existing tests was 5.59, 0.9682 and 0.9779, respectively. The values of statistical indices showed a high agreement between numerical and experimental results. So, after identifying the power of FLOW-3D in simulating the flow, by choosing a discharge and performing simulations on different models, a wider examination of numerical results was considered. This means that the software was used as a virtual lab and other conditions that was hard to create in the laboratory, were created in the software. By simulating and obtaining numerical results, the effect of different geometric conditions of the trapezoidal broad-crested weirs, including the upstream and downstream face slope, weir crest length , etc., was investigated on various hydraulic parameters, including the location of critical depth formation, discharge coefficient, head loss, etc. The results of these studies showed that, decreasing upstream face slope , increased discharge coefficient and lead the critical flow condition to take place Farther from the beginning of the weir crest, but the change in the head loss of flows from the weir does not occur, while the change in downstream face slope, will not have much effect on the amount of discharge coefficient and the location of critical section, but will lead to a change in the head loss. By decreasing the downstream face slope of the weir, the head loss decreases. In addition, increasing the weir crest length, leads to The head loss decreases as well. Keywords : broad-crested weirs, FLOW-3D, RNG K-e turbulence model, computational fluid dynamics, discharge coefficient (Cd), critical section