Abstract: Emissions of PM_2.5 from burning of wheat straw, corn stalks and rice straw were quantified with the aid of FACTSAGE and effects of oxygen supply and temperature during the combustion process on emissions of HF, HCl, SO_x and NO with smoke were explored in an attempt to define proper conditions for burning of bio-materials. Results show that as crop straw contains much F and Cl, burning of the material generates a large amount of HF and HCl. In order to control the generation of F/Cl compounds from burning of bio-materials, temperature of the combustion should be controlled at 1 000-1 100 ℃, and oxygen supply should be from natural air. When oxygen supply is too low, more ammonia and hydroxides will be generated and emitted with the tail gas, while it is too high, more sulfur oxides and nitrogen oxides will, causing formation of secondary aerosol,PM_2.5 and then environment pollution.