A numerical model was established to investigate the lateral mass transfer as well as the mechanism of bed-inventory overturn inside a pant-leg circulating fluidized bed (CFB), which is of great importance to maintain safe and efficient operation of the CFB. Results show that the solid loading along the central line of the pant-leg CFB is promotional to the lateral mass transfer across the central line as well as the bed-inventory overturn. Although the lateral pressure difference generated from lateral mass transfer inhibits continuing lateral mass transfer, providing the pant-leg CFB with self-balancing ability to some extent, the primary flow rate change due to the outlet pressure change often disable the self-balancing ability by continually enhancing the flow rate difference. As the flow rate of the primary air fan is more sensitive to its outlet pressure, it is easier to lead to bed inventory overturn. While when the solid particle is easier to follow the surrounding air flow, the self-balancing ability can be more active. (C) 2011 Elsevier B.V. All rights reserved.