Abstract: Raw material and kibbling material and biomass pellet were observed by microscopy in order to study the surface morphology mechanism in this paper. The biomass pellets which the raw material were corn straw and sawdust were densified by pellet mill, and the combination style of micro morphology and particles of different raw material and material at diverse stages was studied. The results showed that pellet mill was intermittent compression during production process, and surface morphology mechanism of biomass pellet was layered compressed where the layer spacing was from 25 to 40 μm. The pellet was divided into three layers from the cross section, including the center layer particles as “flat” and the transition layer particles as deformed, and the surface particles as “vertical.” Compared to sawdust pellets, the particle density of corn straw pellets was smaller under the same extrusion pressure. So this study will provide important theory basis to design the biomass molding equipment.