This study investigates the flow of a semicircular labyrinth weir in an open channel by experimental and numerical methods. The experiments were carried out in a channel with a length of 3.5m and width of 0.25m and 0.3m height under five different flow rates. Five different discharge values over the weir were used. In each experiment, flow rate and flow depth were measured. Numerical processes solved using mathematical equations of fluid flow through the computational fluid dynamics using ANSYS FLUENT code. The Volume of Fluid (VOF) model is designed for the case of water and air-immiscible faces. Standard k-epsilon turbulence models were tested. A mass balance result indicates that the maximum error between the inlet and outlet discharges of the main channel does not exceed 12% for discharge values of 4.31 L/sec.  The results indicate that by increasing the discharge flow rate, the percentage of error decreased to 0.4% for discharge, 14.6 L/sec. The findings show that the free water surface profile obtained from the numerical model compared to experimental values complies well with the experimental results.