Epoxidation of cyclohexene to cyclohexene oxide was studied in a new type reactor-the ultrasound airlift loop reactor. The influences of ultrasound intensity, molar ratio of isobutyraldehyde to cyclohexene and oxygen gas flow rate on the conversion of cyclohexene and selectivity of cyclohexene oxide were investigated and discussed, and the optimal operation condition was found, under which 95.2% conversion of cyclohexene and 90.7% selectivity of cyclohexene oxide were achieved. The ultrasonic airlift loop reactor utilizes the synergistic effect of sonochemsitry and higher oxygen transfer rate. Possible reaction mechanisms were outlined and the reason of ultrasound promotion of epoxidation reactionwas analyzed.