Abstarct: Side weirs are common structures, used as control structures in irrigation system and conveyance channels. The fluid flow of side weirs is a spatially varied flow with reducing discharge. Numerous physical models of these weirs were built and considered in experimental studies. Compound triangular-rectangular sharp crested side weirs are known as one of side weirs. In this research, the parameters affect the discharge coefficient of side weirs were investigated. These parameters include longitudinal slope of channel (s_0), the flow upstream Froude number, the ratio of weighted crest height of the weir to upstream water depth and the proportion of weir length to flow depth in upstream of weir. The experimental results for three slopes (0.001, 0.002, 0.003) in subcritical conditions showed that the effect of channel longitudinal slope on computational discharge values was insignificant and could be neglected in dimensional analysis which does not effect on accuracy of computation. To estimate the discharge of compound side weir, the discharge coefficient was obtained and compared with experimental results which showed an appropriate accuracy of calculation. To benefit from the advantage of time saving and economic considerations, the flow-3d software was used to simulate the flow around the side weir. The RNG K-ɛ turbulence model was employed in numerical modeling. The purpose of this research was to compare the numerical and experimental results baxsed on the value of weir discharge. This comparison showed maximum that the difference between experimental and numerical results was %0.83 – %1.44 showing confirming the validation of modeling procedure.