White-fleshed dragon fruit which is well-known for being a fruit high in important nutrients has been one of the objects of post-harvest preservation attention. In this work, to shorten drying time, thereby reducing energy costs and improving the quality of drying products, a theoretical and experimental study of ultrasonic pretreatment impacts on the drying process for white-fleshed dragon fruit is carried out to assess the applicability of this treatment technology. The experimental observations show that ultrasonic pretreatment technology has an insignificant impact on the total color difference of the product. However, ultrasonic pretreatment technology can decrease the drying time from 10 to 60 min, corresponding to the ultrasonic treatment time of 30–60 min. Additionally, the theoretical model is developed based on the concept of effective moisture diffusivity to describe the drying process. The numerical results indicate that the effective moisture diffusivity is enhanced by the ultrasonic pretreatment from 33.5% to 109%. It implies that employing ultrasonic pretreatment yields better product quality and improves the energy-saving potential.