Abstract: The measures in terms of alkali treatment, silane coupling agent modification and combination of alkali treatment and silane coupling agent modification were used to modify bagasse (BF). Various modified BF were blended with polylactic acid (PLA) to prepare BF/PLA composites. TGA, FTIR and SEM were used to study the thermal stability of BF/PLA composites. Flynn-Wall-Ozawa (FWO) method and Kissinger method were used to investigate the thermal decomposition kinetics of BF/PLA composites, respectively. The results show that the thermal stability of BF/PLA composites is associated with the structure of BF and the interfacial compatibility of BF/PLA composites. The alkali treatment makes BF fibrillated and reduces its heat resistance, as impedes the increasing of thermal stability and mechanical properties of BF/PLA composites. The silane coupling agent modification improves the interfacial compatibility between BF and PLA, resulting in the increasing of thermal stability of BF/PLA. In the compared BF/PLA composites, the silane coupling agent modification affords most contribution to the increasing of thermal degradation activation energy and mechanical properties of BF/PLA composites, while the combination of alkali treatment and silane coupling agent modification affords second contribution.