Pomegranate peel is an easily available and inexpensive industrial by-product which is rich in polyphenols. In this study, ultrasound-assisted extraction method was used to extract polyphenols from pomegranate peel. The technological parameters were optimized and the composition and content of polyphenols from pomegranate peel were determined by high-performance liquid chromatography (HPLC). The changes of pomegranate peel surface after ultrasonic treatment were also studied. The results showed that with ultrasonic assistant conditions, water as a solvent, had a higher yield of polyphenols, which was better than other organic solvents such as methanol. Therefore, water was used as a solvent for subsequent research. In the optimal conditions of liquid-solid ratio (mL∶g) 60∶1, ultrasonic power 400W and ultrasonic time 25min, the optimal yield of polyphenols was 39.30mg/g (using gallic acid as the standard), which was higher than that of conventional solvent extraction method (32.58mg/g). HPLC analysis showed that the content of punicalagin in pomegranate peel polyphenols was highest, followed by punicalin. Ultrasonic treatment could greatly enhance the extraction effect. The microscopic observation on the surface of pomegranate peel showed that ultrasound could significantly destroy the surface of pomegranate peel and affect the integrity of plant tissue, thus releasing more polyphenols.