Circulating fluidized bed (CFB) gasifiers are advantageous for transforming carbon-based fuels, particularly biomass materials, into product gas, due to a good mixing between solids and gas which improves heat and mass transfer characteristics. In this paper, an Aspen Plus model of integrated biomass gasification-methanol synthesis system was developed to study the influence of working conditions on methanol yield. To enhance the accuracy of the model presented, two FORTRAN subroutines (bed hydrodynamics and reaction rates) were coupled to the computer-based model. Results showed that the presence of steam increases methanol yield, as by increasing the S/B from 0.2 to 1.0 (wt/wt), the methanol yield increases from 2.31 to 9.95 (g/kg biomass) for T-g = 700 degrees C, from 4.02 to 12.01 (g/kg biomass) for T-g = 800 degrees C, from 6.02 to 14.01 (g/kg biomass) for T-g = 900 degrees C. It was also found that the biomass particle size has a minor influence on the methanol yield.