The invention discloses a radio frequency and microwave drying method for preventing ultrahigh moisture grain from mildewing. According to the method, before the newly harvested ultrahigh moisture grain is put in a warehouse, preliminary cleaning, hot air drying, tempering, radio frequency and microwave drying and tempering are performed, so that the moisture content of the grain is reduced to 13.5-14%, and then the grain is delivered into the warehouse for storage. On the premise of guaranteeing dry quality of the grain, through radio frequency and microwave drying, mold spores of the grain are restrained from growing, the moisture reduction rate of a grain drying machine is increased, the uniformity of the grain drying machine is improved, the purchasing and storing efficiency of a grain storage enterprise is improved, the situations that at grain concentrated harvest time, the grain heap heating and mildewing are caused by high moisture, then the quality of the grain deteriorates, and potential safety hazards are caused are reduced, and the radio frequency and microwave drying method has significant economic benefits and social benefits.