Abstract: To shorten the vacuum freeze drying time and improve the efficiency of drying,the effect of ultrasonic pretreatment on the typical pip fruit-apple was studied. Taking the freeze drying time and rehydration ratio of dried apple slices as the evaluating indexes,to optimize the ultrasonic technology from the aspects of ultrasonic power,ultrasonic temperature and processing time,single-factor and orthogonal experiments was used in this paper. Color,texture and other quality indicators of dried apple slices after ultrasonic pretreatment were also tested in this paper. The results showed that an optimized strategy( ultrasound power 200 W, ultrasound water temperature 35 ℃,treatment time 10 min) by orthogonal test could reduce the drying time and improve the rehydration ratio. Quality test results showed that the dried apple slices prepared by ultrasonic pretreatment had higher VCretention amount,more white color,and more loose.