Biomass is one of the most clean and renewable energy resources. Researchers give more and more attentions to the biomass because it can effectively reduce the amount of greenhouse effect due to its zero emission of carbon monoxide. From biomass utilization technologies, biomass gasification is an attractive mechanism for utilizing effectively. Despite the application of fixed bed flow gasification on larger scales, the reaction rates in the hot conversion zone are almost unknown. But the knowledge of the rates of the gasification reactions at high temperature and high pressure is crucial for the detailed design and optimization of the gasifier. This work was focusing on the simulation of the biomass (coffee bean husk and rice husk) gasification process based on the kinetics of the gasifier and to investigate the produced syngas composition. The ASPEN PLUS simulator was used to investigate the effect of operating parameters on composition of product gas. The gasification process usually begins with the drying process, and then followed by pyrolysis. The pyrolysis process leads to breaking down of the biomass into solid matter, gaseous mixture (mainly CO2, CO, CH4 and H2) and liquid matter. The main focus on biomass gasification process is to efficiently convert the entire char constituent into gaseous product of the syngas by using either steam or CO2. The simulations include; gasification temperature, pressure, reactor volume, Equivalence ratio and moisture content have been investigated. From the result of sensitivity analysis increase the temperature the production of H2 and CO and the increase of moisture content of the biomass the lower heating value of the producer gas decrease. Based on the obtained result the maximum lower heating value of syngas was obtained at the gasification temperature of 8000C, steam to biomass ratio of 0.1, pressure of 1 bar, 0.05 of moisture content and 0.02 m3 of reactor volume.