In China, there are great difference in temperature and humidity in different regions. During the storage time, the characteristic of biomass pellet fuel will change, so the application of the fuel will also change. The corn stalks and wood pellet were tested with different storage method, temperature and humidity. The results showed that during the storage time, the temperature, humidity and storage method were the main factors which affected the total moisture of pellet fuel. When the humidity was larger than 70%, the corn stalks will appear mildew. The wood pellet will crack and mildew under the condition of high temperature and humidity.