Aiming at solving the shortcomings of low dilution ratio, short residence time and bad portability of the existing dilution channel sampler, the flue gas dilution sampler for biomass fixed combustion source was developed by using the principle of multistage dilution and jet, according to numbers of atmospheric particulates and characteristics of mass distribution in high temperature flue gas. The sampler consists of five parts: sampling gun, first level dilution system, second level dilution system, clean air making system, impact sampling device and display control system. The proposed sampler has good airtightness, high dilution ratio, stable heat preservation performance and good control precision. The biomass fixed combustion source of flue gas dilution sampler was applied on the wood molding testing. Test results show that the proposed device could simulate the dilution and condensation process of combustion source flue gas which emissions into the atmosphere environment with dilution ratio of 30 and residence time of 90s. The atmospheric particulates in eight different particle sizes were obtained, in which the mass of particle size of 0.4~1.1μm took 55.5%~68.1% of the total mass of atmospheric particulates. The study found that the proposed sampler has a good effect on the atmospheric particulates with diameter less than 1.1μm.