The loop-seal (LS) of a circulating fluidized bed (CFB) reactor is the heart of the system and is still under consideration due to complexities in both two-phase flow and the geometry. The LS controls the solid circulation rate (SCR) of particles that is crucial for the stable operation of a CFB system. In this study, the effect of the aeration rate on the circulation rate of two-chamber LS for a 10 MWth CFB gasification system is examined. The influence of aeration rate supplied to the recycle and the supply chambers of the LS is investigated in detail with 44 different cases using computational particle fluid dynamics (CPFD) method. Barracuda VR software is used to model the whole CFB system with non-reacting isothermal flow assumption. The solid circulation rates are investigated for various aeration rates corresponding to different operating regimes. The stable and unstable operating conditions are identified according to monitored pressure fluctuations. Moreover, three regimes are revealed based on the analysis of differential pressure between two chambers of LS. It is found that the region for the stable operation, corresponding to higher SCR and lower pressure fluctuations, exists for a certain range of aeration rates and the aeration ratio between two chambers of LS.