High dispersion of muzzle velocity due to the unstable burning of propellant grains in a small scale combustor is an unavoidable problem for the low-pressure and short-barrel launch such as the micro air vehicle launched by guns, missile launchers. A dual-chamber system with different structures is designed to overcome this problem. This paper aims to clarify the different multi-dimensional flow and energy conversion behaviors of the combustion gas and propellant grains in two typical structures of dual chambers with a propelled body. Combining the two-fluid model (TFM) and the lumped parameter method (LPM), a coupled approach is proposed to describe the gas-solid flow with reaction in the dual-chamber system, which takes into account gas production, interphase drag, intergranular stress, and heat transfer between two phases. Experimental and numerical results indicated that the two-phase flow and propelling characteristics of both serial and parallel structures are similar in general. The propelling capabilities such as the muzzle velocity and the energy conversion efficiency in the parallel dual chamber system are better than those in the serial structure. But the serial structure is greater benefit to reduce the packing of particles and the projectile acceleration. The narrow zone between two chambers in the parallel structure can develop a vortex in the low-pressure chamber, but rarely affects the movements of particles because of the high-speed jet flow and the limited time. The results present deep understanding of two-phase flow behaviors in different structures of dual chambers. The findings of the study will be applied to improve the design and performance of dual-chamber launchers. (C) 2016 Published by Elsevier B.V.