Ultrasonic-assisted hydrodistillation extraction (UAHE) essential oil from lemon peel was investigated. On the basis of single-factor test, response surface methodology was applied to optimize the parameters of extraction, including ultrasonic power, solvent to material ratio, ultrasonic time, and distilling time on the yield of essential oil. Meanwhile, the volatile composition was analyzed by GC-MS. In addition, the microscopic structures of material before and after various extraction methods are observed to clarify extraction mechanisms. The optimal extraction conditions were ultrasonic power of 320 W, solvent to material ratio of 15.5∶1 (mL/g), ultrasonic time of 36 min, distillation time of 140 min. Under this condition, the oil yield was up to 1.97%. Totally 26 compounds were identified accounting for 96.16%, of which limonene was the major constituent. Scanning electron microscopy revealed that ultrasonic technique efficiently promoted the release of essential oil by breaking down the cell structure of lemon peel. Moreover, essential oil extracted by UAHE was quantitatively (yield) and qualitatively (chemical composition) similar to those obtained using hydrodistillation extraction. Therefore, UAHE essential oil of lemon would be an effective method.