The centrifugal fan is the most widely used because it can efficiently move large quantity of the gas over a wide range of pressures. The flow that enters throughout the impeller is analyzed by using a streamline curvature technique, this method used for a compressor, by neglect the term of gas density change. The turbulent flow is modeled by using algebraic eddy viscous model which based on the mixing length, the turbulent model is applied on the hub to shroud stream surface. The shock in the present work is form by increasing the volume flow rate in put to the impeller .The impeller that chosen in this work is the impeller of the pre-heater fan in the heating system of clinker in AL-Muthanna factory of cement, which has back curved blade. The results prove that the increasing in the volume flow rate (forming shock losses) has an effect on the velocity profile and static pressure, so that where the volume flow rate increase the velocity profile increase and static pressure decrease.