An investigation of flow reversal of mixed flow in a three dimensional channel is studied numerically. At a high Richardson number, natural convection dominates the flow and thermal fields of mixed convection. Behaviors of the residual mass flow rate produced by the difference of the strength of natural and forced convections coexisting in mixed convection are worthy to be examined deeply for industrial applications. Due to the necessity of considering the fluid compressibility, methods of the Roe scheme, preconditioning and dual time stepping are adopted to solve governing equations. The results show that at a high Richardson number situation, via the outlet in large quantities of fluids are sucked into the channel from the outside that causes the flow and thermal fields in the channel to be unsteady and vice versa. (C) 2013 Elsevier Ltd. All rights reserved.