Abstract Based on the chemical process simulation software Aspen Plus, the biomass pyrolysis model was established by Ryield reactor. In the Ryield reactor, a compiled fortran subroutine was embedded to calculate the yield of reaction product. With rice straw as the sample, the model calculated the product yield and component contents of pyrolysis gas under different temperatures. The results indicate that with the temperature increases from 350 o C to 600 o C, the yield of coke and bio-oil gradually decrease, while the yield of non-condensable gas gradually increases. Meanwhile, among the non-condensable gas components, the volume fraction of CO rapidly increases, the volume fraction of CO 2 rapidly decreases, and the volume fraction of CH 4 increases slowly. Compared the calculated values with the experimental values, the results show that biomass pyrolysis model can simulate the variation of biomass pyrolysis effectively and it can provide some reference for the development and optimization of biomass pyrolysis technology.