Abstract: With the cavitation test material,ultrasonic cavitation in high-pressure and dense-phase fluids was explored and the theoretic deduction was probed.According to the experimental results,at the same power of ultrasound,the cavitation test material shows many pores in high-pressure liquid CO₂,whereas,it did not appears in supercritical CO₂.This phenomena shows that ultrasound can generate cavitation in high-pressure liquid CO₂(subcritical station),but not in supercritical CO₂.Based on theoretic deduction,ultrasound can generate cavitation in high-pressure liquid CO₂ due to high vapor pressure of CO₂,reduced the external pressure influence.However,there are no liquid-gas phase boundaries in the supercritical CO₂,hence prohibiting cavitation.