A new integrated CO2 gasification of biomass process is developed using Aspen Plus. The performance of the process is evaluated by determining producer gas compositions, gasification system efficiency (GSE), and cold gas efficiency (CGE). In this gasification process, a reformer and a CO2 absorber are introduced to enhance CO and H-2 and to reduce CO2 concentrations in the producer gas. The process optimization is performed by varying CO2 to carbon ratio (CO2/C) at different pressures, steam to carbon ratio (S/C) and equivalence ratios (ERs). It is showed that the introduction of CO2 to the gasification process has a positive effect on the CO concentration, a negative effect on the H-2 concentration, and minimum effects on CGE and GSE. It is also found that high pressure has adverse effects on CO and H-2 concentrations in the producer gas, CGE and the GSE. However, high pressure slightly enhances the H-2/CO ratio of the producer gas. A positive effect in term of H-2/CO is observed on higher steam injections. The gasification of the microalgae exhibits the best performance in term of H-2/CO ratio and CGE as compared to the gasification of other biomasses. (C) 2017 Elsevier Ltd. All rights reserved.