Numerical and experimental study of the gasification of raw and pretreated (torrefied and carbonized) cotton stalks were investigated. The experimental results were used to calibrate the quasi-equilibrium model by multiplying the equilibrium reaction constant with coefficient varying from 0.01 to 10 and by fixing the methane molar fraction. Values varying from 0.15 to 0.7, 0 to 0.8 and 400 to 900 K were considered for air equivalence ratio (ER), the ratio of steam to fuel (SF) and the temperature of steam respectively. LHV and energy efficiency decreased from 4528 kJ Nm− 3 and 73.5% for the raw cotton stalks to 3984 kJ Nm− 3 and 68.9% for torrefied cotton stalks and to 3815 kJ Nm− 3 and 69.6% for carbonized cotton stalks. The energy efficiency was improved by steam injection to 80, 78 and 75% for the gasification of raw, torrefied and carbonized CS respectively due to the increase of H2 and CH4. The air–steam gasification was more efficient to air gasification at a temperature of steam over than 500 K for raw cotton stalks. However, only the air–steam gasification of pretreated cotton stalks was recommended since it has the net energy efficiency (which consider the steam energy) superior to 60%.