As a byproduct of activated sludge process, excess sludge has become one of the current problems in the field of environmental protection for its yield huge、high moisture content and easy to pollution. In this study, the joint technology combining ozone with ultrasonic was applied in treatment of excess sludge by strong ozone oxidation and prominent ultrasonic cavitation. The effect on lysis excess sludge cells was explored comprehensively. The lysis mechanism of excess sludge cells degraded by ozone + ultrasonic was revealed by analysis of three-dimensional spectral fluorometer, optical microscope and scanning electron microscopy (SEM). The results showed that the MLSS was 22.92% lower than the untreated sludge, the SCOD and –N content in the supernatant of the sludge was 1792 and 105.77 mg/L, which was 96.49% and 17.67% higher than the untreated. The supernatant of treated excess sludge contained macromolecular organic matters composed of proteins, polysaccharides, humic acids, and fulvic acids, etc. The whole process of lysis cells of excess sludge degraded by ozone + ultrasonic could be inferred that the microbial particles of excess sludge were exposed after EPS destructed, and then the cell walls of these exposed microbial particles were broken so that a great number of intracellular materials were released. Furthermore, these intracellular material composed of macromolecular organic matters were degraded into small molecule organic matters, H₂O, CO₂, etc. Finally, the excess sludge was treated gradually by ozone + ultrasonic.