Junction in open channel flow points out any side water secession from natural or artificial channels. In the last decades, comprehensive theoretical and experimental investigations on the dividing flow in open channel junctions have been executed to understand the characteristics of this separating flow. In this research, a three-dimensional turbulence model by fluent software used to replicate the flow characteristics of a 90º open channel junctions for two geometries. One is with equal width and horizontal bed and the other is field canal junction with irregular section. The modeling is based on the Navier-Stokes equation and κ-ω turbulent model. Comparing prepared to the numerical solution, the analytical model and the field works with published experimental data. The comparison showed that the numerical solution gave good agreements with maximum discrepancy 1.620% for rectangular sections and 0.718% for irregular sections than the published experimental data. The analytical solution gave a large error than numerical with a maximum discrepancy of 2.95% for the rectangular section and 11.485% for irregular sections than the published experimental data. A proposed relation between discharge ratio with upstream Froude number and depth ratio for the irregular section is suggested. The proposed equation has a maximum discrepancy equal to 0.433% with reference to the field data recorded.