33.2。 A pulsed vacuum drum dryer was designed. This machine consisted of a drying drum, heat system, rotary joint, control system, vacuum system and drive system. The pressure in the drying drum can be changed between vacuum and atmospheric pressure by opening or closing an electromagnetic valve. The drying drum can increase the load of materials, and at the same time can make heating more uniform by rolling. So, the efficiency of the machine can be increased. The experimental results of centennial seedless drying demonstrated that the machine could produce raisins with moisture content of 16.4% (w.b.) and acid-sugar ratio of 33.2 in 12h. when the pressure was 7kPa, vacuum drying was 20 min and atmospheric drying was 4 min for one cycle, drying temperature was 60℃.