Abstract: Research and application on screening in China are mainly focused on coal, metallurgy, chemicals, building materials, and so on, only a few researches on the field of biomass energy. Biomass energy research is mainly focused on raw material obtaining and process, which can??t solve small impurity removal problems after straw harvest. Therefore, this article carried out the comparative tests of thermal characteristics on corn stover feedstock with different sizes, studied the impact of dust and other fine particulate matter on raw materials quality of corn stover, and analyzed the proportion of impurities with different particle sizes and their impacts on raw materials; the best sieve size range of raw materials was put forward so as to improve the purity of raw materials, and optimize the impurity screening equipment connecting between mill and molding machine. A series of experiments were done. At first, different corn straw materials, which were less than 10 mm particle size, should be divided into 9 size classes through sieve analysis; secondly, different size particles as material were utilized for thermal characteristic measurement and sedimentation experiments; thirdly, the proportion and the effect of fine particulate impurities in different corn straw materials were analyzed; at last, dust contents of 2 kinds of materials whose sizes were less than 0.2 and 0.33-0.2 mm exceeded 50%, and the quantity represented 3.39% of the total sum of such 2 kinds of materials. Therefore, the best suitable material size range is less than 0.33 mm compared to the other straw materials. Through the results of above analysis and a large number of reference documents, the sieve in this study were modified and processed from the former drum sieve. The structure of sieve also could be optimized, and its parameters were as follows: Sieve tube length was 1000 mm, screen cylinder diameter was 500 mm, screen cylinder inclination angle was 10°, rotation speed was 34 r/min, and sieve hole diameter was 0.33 mm. The comparative experiments and economic analysis based on this equipment were conducted. The results showed that the volatile matter and calorific value of pellets through the sieve process were improved significantly, and the ash content was reduced by 25.21%, which greatly declined the material??s molding wear risks to briquette machines and slagging risks to combustion devices. The economic value of this briquetting fuel increased to 563.5 yuan/t, which increased by 6.91%. The method that the sieve is considered as the first phase at the briquette forming can improve the purity of the material, and ensure the quality of fuel formed from corn straw. This thesis is expected to propose a screening technology and equipment suitable for Chinese large-scale production of biomass briquettes, to provide technical support for cleaning process, and to provide an important basis of parameters for the energy utilization of the straw.