A new integrated co-gasification of coal and biomass simulation model was developed using Aspen Plus. It consisted of three main processes: (i) gasification, (ii) reforming and (iii) CO2 absorption. The simulation exhibited a good accuracy when compared to the experimental values under same operating conditions. In co-gasification evaluation, a low-rank Indonesian coal and N. oculata microalgae biomass were considered as feedstocks. The parametric study was carried out using various biomass to coal ratios at different pressures. The performance of the overall process was evaluated in terms of syngas composition, gasification system efficiency (GSE) and cold gas efficiency (CGE). The reforming and CO2 absorption steps enabled the process providing high purity syngas. The increase of biomass/coal ratio enhanced GSE while decreased CGE. High pressure operation was found to be unfavorable for producing high quality syngas as the increase of pressure affected the gasification. Overall, the co-gasification of biomass/coal is a promising approach to utilize low-value coal and biomass feedstocks to produce high value syngas and contributes to minimization of greenhouse gas emissions.