Abstract: In this paper, the beef longissimus dorsi muscle was used as experimental material and subjected to ultrasound-assisted curing. The effects of different ultrasonic times (0, 15, 30, 45, 60 min, 300 W, 30 kHz) on the quality characteristics and protein structure of beef strips before fermentation and beef jerky after 6 days of natural fermentation were investigated. The results showed that increasing the ultrasonic time significantly increased the moisture content, water activity, pH and salt content and decreased the shear force in beef strips before fermentation and beef jerky after 6 days of natural fermentation (P<0.05). In addition, the structure analysis of myofibrillar protein in beef strips after ultrasonic treatment showed that the myofibril fragmentation index rose, surface hydrophobicity, carbonyl and active sulfhydryl content increased, and total sulfhydryl group content decreased with the increase of ultrasonic time (P<0.05). The a^* values of the treatment groups were significantly lower after the ultrasonic time exceeded 30 min (P<0.05), and the differences in beef jerky tenderness were not significant (P>0.05). In conclusion, to avoid excessive oxidation of proteins and waste of energy, an ultrasonic treatment time of 30 min was finally determined as the best treatment condition, which could effectively improve the quality characteristics of beef jerky.