Torrefaction as pretreatment for the thermochemical conversions is one of the profound technologies. In this work, torrefaction-gasification integrated process has been modeled and studied. First, a combination of different torrefaction models was adopted to quantify the ultimate analysis of the torrefied biomass. Then, the torrefied biomass was set as the input to gasification model and the results of gasification were analyzed. Impacts of different torrefaction conditions on gasification were evaluated. With torrefaction-gasification integrated process, composition of syngas was improved. The increase in severity of torrefaction conditions, enhanced the quality of syngas.