Abstract: In this paper, a new flow regime is identified by applying an umbrella-like baffle in a rectangular spout fluidized bed and studied by Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) approach. The simulations indicate the new flow regime features a multistage spouting – first spouting and second spouting. It is studied in aspects of spout robustness, mixing efficiency and formation mechanism. In the multistage spouting, the first spout and second spout always deflect but in opposite directions largely. This dynamic balance of the two spouts enables the high robustness in the multistage spouting pattern. Moreover, the efficiency of the gas–solid mixing is improved as four extra mesoscale particle circulations are formulated, reducing solids residence time in the dense region. The formation mechanism and regulation of the second spouting is also explored. It is indicated that the baffle opening angle of >60° can ensure the continuum and compressible property of particle flow.