Bayberry powder is easy to cake leading to the bad quality during the processing and storage. In order to avoid and lighten caking, the followed experiments were carried out, such as the correlation between water activity and glass transition temperature by differential scanning calorimetry -DSC- and the effects of temperature and relative humidity on caking of bayberry powder. Glass transition temperature of bayberry powder had linear correlation with the water activity, Tg= 45758-1688 aw -R2=08631-. The appropriate processing temperature and relative humidity of bayberry powder should be lower than 25℃ and 22%, respectively. Collapse, stikiness, and caking were the three steps of bayberry powder caking.