Abstract: Wear trial of roller assembly was carried out to solve the problem with which the key accessory of HM485 biomass pellet mill, e.g. die and roller, was abraded so that decreased the work life and productivity during produce densified biofuel. In this study, the roller assembly was manufactured by steel 45 with carburization treatment and the carburized layer depth was 3 mm, and the working life was 200 hours. The roller assembly was rapid abraded and became wear failure because of silicate minerals, impurities and moisture in raw materials. The principle of wear failure was studied with S-570 scanning electron microscope, the results showed that the wear depth of roller assembly which closed the feed side was up to 4.2 mm, and it was deeper 1.2 mm than other sides. The principle of wear failure is mainly adhesive wear and abrasive wear, and there is stress corrosion cracking in the abrasion surface which is close with the junction of carburized layer and substrate.