The effect of ultrasonic pretreatment on drying properties of lemon slices was studied， with the dry base moisture content， drying rate， rehydration rate and vitamin C content as the main indicators. Results showed that the drying rate of hot-air drying lemon slices increased， the drying time decreased by at least 20% and the energy consumption of hot air drying stage significantly reduced after ultrasonic pretreatment. The shorter the probe ultrasonic pretreatment time within the experimental range， the higher the drying rate. However， the longer the ultrasonic cleaning pretreatment time within a certain range， the higher the drying rate. Ultrasonic pretreatment not only reduced the loss of vitamin C during hot air drying of lemon slices， but also improved the rehydration rate of dried products. The longer the time of probe ultrasonic pretreatment， the greater the loss of vitamin C， and the lower the rehydration ratio， so the pretreatment time should be shortened in the application. With the increase of ultrasonic cleaning pretreatment time， content of vitamin C in dried lemon slices decreased gently and the rehydration ratio gradually increased， while there was no significant change after the ultrasonic pretreatment time increased to 11 min （P<0.05）. The content of vitamin C in dried lemon slices pretreated with probe ultrasound for 3 min and dried by hot air for 160 min was 32.93 mg/100 g and the rehydration ratio was 4.61 ± 0.08. Moreover， the content of vitamin C in dried lemon slices pretreated with ultrasound cleaning for 11 min and hot-air drying for 160 min was 29.70 mg/100 g and the rehydration ratio was 4.60 ± 0.13.