The osmotic dehydration of longan sarcocarp enhanced by ultrasound was probed. The influence of the main process variables, including the time of osmotic dehydration, the time of ultrasound field treat and the intensity of ultrasound field on water loss, solid gain, weight reduction and relative conductivity of sarcocarp cell membrane were investigated. And the empirical dynamic model of osmotic dehydration of longan sarcocarp enhanced by ultrasound field was set up. The results showed that: 1) ultrasound field could enhance the osmotic dehydration process and accelerate the dehydration rate. 2) the empirical dynamic model adequately described the experimental values. The root mean square (RMS) percentage deviation of the model from the experimental data was less than 5%.