Freeze-dried fruits and vegetables can greatly preserve the original nutritional value and sensory quality of the food. However, freeze-dried food are not popular in food consumption field due to low drying rate, long drying time and high energy consumption. In this study, carrots were processed by three kinds of method: UHA pretreatment combined with ultrasonic assisted freeze drying, blanching pretreatment with hot air drying and blanching pretreatment combined with freeze drying. The qualities of carrots after three processes were compared. After UHA pretreatment and ultrasonic assisted freeze drying, the volume of carrots sample was decreased by 17.78%; puncture force in external and core decreased, and the change of color were relatively small; carotene content was (69.51±0.20) mg/100g, Vc content was (48.02±0.62) mg/100g and rehydration rate was 6.93, which were the highest in all treatments. The ultrasonic group had better performance in terms of product's texture, carotene content, Vc content and rehydration rate, which showed the superiority of ultrasonic technology in the freeze drying of fruits and vegetables.