Steam gasification of biomass with in situ CO2 sorption provides a promising route for the H-2 rich syngas production and negative carbon discharge; hence, many scenarios have been proposed to realize this technology. In this work, a two-stage fluidized bed (TSFB) gasifier is put forward in comparison with the normal dual fluidized bed (NDFB) gasifier to realize the calcium enhanced gasification of biomass, and the corresponding one-dimensional models that couple the reaction kinetics and the fluid hydrodynamics are set up and validated. Then, effects of different key operation conditions on the mole fraction of species i (f(i)) in the producer syngas, the conversion of steam (R-w), the conversion of char (R-ch), the carbon capture ratio (Re), and the cold gas efficiency (eta) of the two reactors are analyzed and compared. It is found that the H-2 mole fraction (eta(H2)), R-ch R-w, R-c, and eta of the NDFB reactor are close to 70%, 35%, 35%, 70%, and 40%, respectively, and those of the TSFB reactor are close to 85%, 100%, 70%, 65%, and 60%, indicating that the TSFB reactor proposed in this work is promising to generate the H2 rich syngas and to remove CO2 from the atmosphere.