Abstract: Abstract: Biogas slurry is a high-quality organic fertilizer, which is rich in nitrogen (N), phosphorus (P), potassium (K), amino acids, humic acid and plant hormone. However, only small scale of biogas slurry has been utilized because the limited knowledge of physical characteristics of slurry influences its filtration efficiency. So understanding the composition of particles in biogas slurry is very necessary to realize large-scale application of biogas slurry. The composition of particles in biogas slurry from an continuous-running biogas engineering was studied by using hierarchical filtering methods. The biogas engineering adopted semi-continuous fermentation technology, a typical fermentation technology in East China. Fresh biogas slurry was filtered with the sieves of 20, 40, 60, 80 and 100 meshes in turn, and then slurry particles were collected from the surface of these sieves. The shape of slurry particles was observed by Olympus digital microscope, and their size and distribution were analyzed. And the composition of particles and the nutrient contents for different depth of slurry layers were also studied after slurry was stored for 3 d. The data were analyzed by Excel 2007 and SPSS 19.0. The results showed that mycelium was found in the particles filtered out by the sieves of 80 and 100 meshes, and the number of mycelium filtered out by the sieve of 100 meshes was significantly more than 80 meshes (P=0.008). The proportion of particles filtered out by 80-mesh sieve was the most, which accounted for 53.1%. These may be main causes of slurry filtration blockage when using the screen mesh with small aperture. By synthesizing the factors of particle number, size and shape, it could draw the conclusions that the aperture of 60 meshes is suitable for slurry filter. The study of maximum size of particles passing through the filter found that part of particles or mycelia which were more than filter aperture size still could pass through the filter, which made pipe blockage possible during biogas slurry application. The maximum size of particles passing through 40-mesh sieve (aperture size 0.42 mm) was 1.1 mm, the maximum size of particles passing through 60-mesh sieve (aperture size 0.25 mm) was 0.7 mm, and the maximum size of particles passing through 80-mesh sieve (aperture size 0.177 mm) was 0.4 mm. To avoid pipe blockage in the subsequent biogas slurry irrigation, the size of the sprinkler pipe mouth should be increased appropriately. Particles in slurry subsided to the bottom during slurry storage. Under the condition of slurry storage depth of 1 m, particles mainly concentrated in the 70-100 cm layer after 3-day storage. Different depth of biogas slurry layers had no significant difference in total phosphorus (TP), potassium (K) and chemical oxygen demand (COD) contents, which means that the depth of biogas slurry doesn't need to be considered when it is utilized. Nevertheless, the content of total nitrogen (TN) in biogas residue was significantly lower than that in slurry, but TP and TK contents in biogas residue were extremely significantly higher than that in slurry, especially the content of TP was 87 times that of slurry. P content should be as the basis of biogas residue application. These results above can provide a reference for the establishment of large-scale and high-efficiency biogas slurry application project.