Abstract: The co-pyrolysis behavior of two low rank coals (Inner Mongolia Xinghe coal, Xiaolongtan coal) and three common biomasses (straw, sunflower, apple tree branches) was investigated by non-isothermal thermogravimetric analysis and fixed bed experiments. The results show that whether the co-pyrolysis of biomass and coal has synergistic effects is closely related to the type and the adding amount of biomass. The synergistic effect during the co-pyrolysis of Inner Mongolia Xinghe coal and apple tree branches at the mixing proportion 2∶1 is found to be the most obvious, which is further proved by an analysis of co-pyrolysis products in a fixed bed. The analysis results of tar component show that the content of oxygenated compounds in tar increases, but the amount of hydrocarbons decreases. The co-pyrolysis can increase the yield of tar but it cannot improve the quality of tar.