Drying operation involves wide fields of national economy. It is not only the indispensable basic production link for a large batch of industrial and agricultural products, but also provides guarantee for safe custody and application of agricultural products. Meanwhile, the drying consumes energy very highly in China, the energy for drying accounts for about
12% [1] of total energy consumption of national economy. The drying for agricultural products is one of the main fields. High energy consumption is one of the major reasons influencing the development of the drying industry, while the drying for agricultural products is the most important treatment link after harvest in the production process of agriculture and also the important step during the processing of harvesting agricultural products. Especially, the t drying is more important in the production process of grain. The harvested grain can be stored under safe moisture, and most of the harvested grain needs drying so as to reach the storage requirements. Guaranteeing the safety of reserve grain directly concerns national economy and the people’s livelihood. Therefore, from this meaning, the grain drying is more important. With the improvement of people’s living standards and the quickening pace of life, convenient and rapid food is more and more popular, and people focus on the quality and safety of food much more. But the convenient food needs many dehydrated vegetables and fruits which must be used after drying. Traditional natural drying is good in quality, but the production efficiency is low, which can not meet the demands. The existing hot-air drying not only consumes large energy, but the drying method has great damage to the product’s color, luster, vitamin C and other bioactive substances. However, the cost for the present drying method with good quality is very expensive (like freeze drying), which causes the contradiction relation between product quality and cost. How to obtain better drying quality and lower drying cost is the actual problem of researchers in the drying industry