To reduce freezing-induced damage, a novel freezing method based on pressurized CO2 pre-injection combined with ultrasound-assistance was developed for quick freezing of pieces of honeydew melon. The samples were first exposed to CO2 at different pressures (0.2 MPa, 0.5 MPa and 0.8 MPa) and then placed in an ultrasound-assisted freezing device. The ultrasonic intensity was 0.15 W/cm2 at 20 kHz. The results indicate that pre-injection of CO2 enhanced ultrasonic cavitation and significantly (p < 0.05) increased the nucleation temperature, thus shortening the freezing time. CO2 combined with ultrasonic assisted freezing can reduce the variation in the state of water in the sample after freezing and thawing. The results of SEM, cryo-microscopy and inverted fluorescence microscopic observations show that the cellular structure of the sample was better protected and the tissue was less damaged by ice crystals. This suggests that CO2 pre-injection combined with ultrasound assist during freezing can effectively control ice nucleation, ice crystal growth and reduce freezing-induced damage.