Flow rate measurements are among the most important operations in modern industries dealing with increasingly expensive fluids such as petroleum, natural gas and water. The accuracy of flow meters depends mainly on their position in a pipe network and their operating conditions. Pipe fittings such as valves and bends generate turbulence and swirl and distort the flow distribution in the pipe, leading to a substantial amount of measuring error. For accurate flow rate measurements, the standards ISO 5167 specify either a sufficient straight piping lengths or the inclusion of a flow conditioner between the flow distortion and the flow meter. Flow conditioners serve to reduce the developing length between pipe fittings and flow meters and to create fully developed flow condition within short distances. In the present study, numerical modeling of the flow development upstream and downstream of the orifice plate which used circle grid fractal flow conditioner has been made. Computational Flow Dynamics techniques have been used to predict the flow development downstream the flow conditioners.