Abstarct: Abstract The piano key weir is a type of hydraulic structure that is used in various ways, including flow measurement in channels, change of flow regime in channels and flood control .One of the most important advantages of piano key weirs compared to linear weirs is the improvement of flow transfer capacity by increasing the length of the crown and as a result, increasing the length of the water passage in a fixed width of the construction without increasing the upstream water head. In general, increasing the length of the crest in the fixed width of the overflow construction will lead to an increase in the number of cycles, which will intensify the negative effect of the local submergence of the outlet key and reduce the effective length of the current passing over the overflow crest, and this problem will only increase Costs in the construction of overflow and economic inefficiency are in the design .The purpose of this research is to numerically model the flow and investigate the effect of simultaneous changes in the number of cycles and the angle of the weir on the flow coefficient by trying to keep the total length of the weir crest and other geometric parameters such as the height of the weir, the ratio of the width of the inlet key to The outlet key is the slope of the sloping surfaces upstream of the inlet key and downstream of the outlet key, as well as the width of the overflow opening (overflow structure) for all models . The purpose of constant consideration of other geometrical parameters in all models, creating equal conditions in all observations in order to investigate as accurately as possible the effects of changing the number of cycles and the weir angle on the flow coefficient and also to achieve the best result (the highest flow coefficient) by spending the same amount (constant length of the overflow crown in all models .(After the investigations, it was found that increasing the overflow angle of the piano key at a fixed length for all models increases the flow coefficient, while increasing the number of cycles at a fixed length for all models due to the reduction of the inlet key water tank area. increasing the contraction of the flow lines and then intensifying the local submergence in the outlet key, the flow coefficient will decrease significantly .Also, among all the weirs modeled in this research, the weir ATPK135-2 is known as the best model and was able to increase the flow coefficient by 47% compared to the linear mode (without curvature) of the PK1.0 piano key weir.