An investigation of a dual-reflection phenomenon of a natural convection induced by a high temperature difference in a three dimensional horizontal channel is studied numerically. Because of a situation of high temperature difference, the Boussinesq assumption usually made in the natural convection problem is no longer available, the effects of the compressibility of fluid on all related factors must be considered. Solution methods of Roe. preconditioning and dual time stepping are appropriate for low speed compressible flow field and combined to solve the governing equations. For saving computation time, the computational process is parallel and 8 processors are used. At the aperture of the horizontal channel, the directions of fluid flows in the upper and lower regions are opposite which results in the reflection problems in the upper and lower regions induced by the large difference between the velocities of acoustic waves and fluids being completely different. The two different reflections phenomena occurring at the same aperture is conveniently named as a dual-reflection phenomenon which has never been investigated. (C) 2009 Elsevier Ltd. All rights reserved.