Abstract: In order to reveal heat and mass transfer mechanism in ultrasonic assisted cooling and freezing processes, a mathematical model of droplet cooling and freezing under ultrasonic was established based on acoustics theory and heat and mass balance. The effects of ultrasonic on droplet temperature, position of liquid-solid interface and droplet diameter were analyzed. Heat transfer induced by mass transfer (due to ultrasonic cavitation effects) and heat generated by ultrasonic thermal effects during the freezing process were analyzed. The results show that ultrasonic cavitation enhances mass transfer on droplet surface, which is beneficial to droplet cooling and freezing. There exists a reasonable loading time for different frequencies and intensities of ultrasonic. The simulation results and experimental data show good agreements with maximum error of 10.6% and minimum error of 0.3%.