Abstarct: Weirs play an important role in regulating water levels, safety and construction costs in hydraulic structures. To increase the efficiency, it is possible to employ labyrinth weirs which can improve the discharge by increasing the weir length at a given width. Due to the construction of the arc in their plan view, the crest length increases for a given channel width and this leads to a higher flow rate and discharge coefficient. In this thesis, coefficient of flow discharge and flow rate of arced trapezoidal labyrinth weirs with vertial walls and half-round crest is studied by using FLOW 3D software and turbulance model k/etta RNG. Furthermore, these parameters are investiagted for arced trapezoidal labyrinth weirs with a sloped wall with two types of flat and half-round crest. Also, triangular, rectangular and circular labyrinth weirs with half-round crest in view of plan are studied as well.The results show that on average, in the range of hydraulic heads, the arced triangular labyrinth weir with angle of 11 degree pass through the most discharge compared to all types of weir. Then, respectively, the arced triangular labyrinth weir with with vertical wall, rectangular labyrinth weir, trapezoidal labyrinth weir with slope wall, triangular labyrinth weir with angle of 24 degrees and, in the end, circular labyrinth weirs have more discharge rate than linear weir. Comparison of results shows that in all labyrinth weirs in the lower head conditions, by increasing Ht/P (headwater ratio), the discharge coefficient is increased until reaches to its maximum value and then decreases.