The pyrolysis characteristics of cellulose was investigated using TGA and TG-FTIR. An modified reaction model was proposed to study cellulose pyrolysis. In this model, the active cellulose (E = 137 kJ/mol) and dehydrocellulose (E = 91.3 kJ/mol) were formed by parallel mechanism. The degradation of the active cellulose was followed by two competitive pathways, this is, one that formed levoglucosan (E = 159.210/mol) and another that formed furan and some low molecular weight products (E = 203.5 kJ/mol). The random scission model was used to describe the kinetics of cellulose pyrolysis. The same kinetic parameters were used for different linear heating rates (10-100 degrees C/min) and isothermal segment conditions. By successfully modeling non-isothermal and isothermal segment data, the model was proved to be credible in describing cellulose pyrolysis.