Aiming at distinct straw in different areas of China, this paper has schemed out a kindly straw-fired boiler which can burn different kind of straws. The 200t/d straw-fired boiler has been taken as subject investigated, when Air to fuel stoichiometric ratio is 1.85, the ratio of primary air and secondary air is 6.5:3.5 and the air temperature is 180°C, different straw in the same furnace arch straw-fired boiler has been burned and related mathematical modeling methods have been established in order to simulate in-bed combustion process using a share software FLIC (developed by Sheffield University Waste Incineration Centre). In the computation out-of-bed gas combustion and furnace arch radiation were simulated by commercial software FLUENT, not only the temperature, velocity and concentration distributing of the top of bed but also the solid temperature profile of in-bed and burning character of out-of-bed have been obtained. The simulation results showed that the calculation is in coincidence with the relative literature data. it has also proved that the furnace arch structure design in this paper is reasonable and useful.