Abstract: To estimate the design and function level of straw briquette boiler, realize secure, stabile and economical operation, adopting direct measurement method and under the normal working condition (α_py=2.20), the double fire grates boiler designed by the authors has been tested. The gas concentration distribution rule of varying with height and depth of the hearth was worked out, thickness of dryness, distillation, oxidation, reduction and dreg layer were analyzed. The gas concentration distribution is more rational on this condition. Secure, stabile and economical operation of the boiler was realized. Combustion efficiency of the boiler reached 98.20%, thermal efficiency reached 74.39%. Meanwhile, the boiler has the function of removing smoke. It lays foundation for optimization design of burning equipment and running adjustment.