With pyrolysis as an attractive way to reduce CO2 and degrade residues, the effect of particle size and heating rate on pyrolysis of capsicum stalks has been investigated by thermogravimetry-differential gravimetric analysis and kinetic studies. Results show that pyrolysis reaction rate increases with increasing particle size. It is supposed that the contents of hemicelluloses, cellulose, lignin, and ash of various particle sizes have significant influence on the pyrolysis of biomass. Meanwhile, high heating rate does not mean high reaction rate, there is a complex competition effect between thermal hysteresis effects and the driving force originated from different heating rates.