Sorghum was pretreated by sole ultrasound or supercritical carbon dioxide (scCO(2)), as well as the method combining both to intensify enzymatic hydrolysis. The effect of the time (1-5h) and temperature (30-70 degrees C) on ultrasonic pretreatment was investigated, and the best condition was determined as 5h and 50 degrees C with the EH sugar yield of 33.69%. The influence of the time (6-48h), temperature (40-80 degrees C), and pressure (15-25MPa) on scCO(2) pretreatment were also discussed in this study. The optimum condition of scCO2 pretreatment was identified as 60 degrees C, 20MPa, and 36h with the EH sugar yield of 43.57%. Compared with the sole ultrasonic or scCO(2) pretreatment, scCO(2) associated with the subsequent ultrasonic pretreatment did not show significant improvement in sugar yield. However, 30MPa was an extremely effective pressure, which led to 45.50% EH sugar yield with 60 degrees C, 6-h pretreatment. Finally, the change of the microscopic structures of the sorghum stalk after the pretreatment was investigated using scanning electron microscope (SEM) and X-ray diffraction (XRD).