Drying has been widely studied as a necessary process in biomass utilization. The steam diffusion law plays an important role in drying kinetics. The drying kinetics of a single biomass particle using Fick’s second law of diffusion was studied in this paper. A parabolic relationship appeared between the critical moisture content and temperature. The critical moisture content decreased with the increase in drying temperature and the initial moisture content. The drying temperature had a significant effect on the effective diffusivity and coefficient of mass transfer during the dramatically falling period of the biomass drying process. However, it was affected by the effective diffusivity and coefficient of mass transfer during the slowly falling period. The initial moisture caused the opposite effect during the different periods. The normalized biomass moisture content generally increased with the increase in drying temperature, and decreased with the increase in initial moisture content. The initial moisture content had an effect on the normalized biomass moisture during the slowly rising period. Meanwhile, the drying temperature had an effect on the normalized biomass moisture during the whole period. The critical moisture content and the normalized biomass moisture content had negative relevant relationship. This study provides some valuable conclusions regarding the biomass drying process.