Abstarct: Side weirs are common hydraulic structures in water transmission channels, Irrigation systems and sewage collection. This structure aslo can be used as flood diversion structure at flooded conditions. Triangular weir can measures low discharges accurately but not suitable for high discharges. therefore compound type of triangular weir is used to both purpose of accurate measurement and ferry high discharges. There have been no study done for sidelong type of compound triangular-triangular weir. So in this study compound triangular-triangular sharp-crested side wires were studied experimentally and numerically in subcritical flow conditions. By Using experimental data and dimensional analysis, effective parameters in discharge coefficient of this weir were specified in direct and De marchi methods and in each methods an equation Presented for discharge coefficient. Results from this equations have suitable adaptation with the experimental results. Besides, effects of changing upstream fruid number on water surface changes along crest of weir( on the crest) was checked.¬ Observations illustrates that with imcreasing the upstream fruid number, water surface changes on the crest of the weir increases. In numerical section, flow over discussed weir was simulated using FLOW-3D software. Due to time constraints and costs needed for laboratory investigations and on the other hand the increasing development of computational fluid dynamics models and the ability of these models to simulate various conditions for the phenomenon under study, more justified will be to use this models. the purpose of this simulation is to evaluate the FLOW-3D software's ability to simulate flow over compound triangular-triangular sharp-crested side wires. Flow situation in this simulation was introduced as turbulent flow to model. Among the available turbulence models in this application, RNG k-ε model as the model proposed by other researchers, was used to solve the equations of turbulent flow. comparison between silmulation results and experimental results,illustrates the suitable accuracy for FLOW-3D model to simulate flow over compound triangular-triangular sharp-crested side wires. So that the values calculated by the software for overflow discharge compare with experimental data had little differences.also surface shape on weir crest was modeled property. also the software could properly calculates the shape of water surface profile on the crest of the wier.