Desiccant is a dehumidification which absorbs moisture in the air .Its principle is to absorb the water molecular into its own structure or to change its chemical structure into another substance by means of chemical method to absorb water molecular . During the ocean transport or storage. The big temperature changes between day and night on the sea make the high-temperature air in the day full of water saturate because of the falling temperature at night.. As a result, the goods usually experience the marine high-temperature climate and comparatively big changes of temperature between day and night which often vary from 0 centigrade to 8 centigrade, with the humidity being able to reach 98percents. This phenomenon is called condensation. The amount of water in the air is 30.4g/m3 , when the temperature is 30centigrade. When the temperature drops from 30 centigrade to 10 centigrade, the amount of water vapor will drop to 15.4g./m3. While the other steam will condemn to water. This is the usually-called "rain in the container", which has a bad influence on the packing. Therefore, a certain amount of desiccants should be used to solve this problem.