Tetrachloroethylene (PCE) aqueous solution was used as the sample to be decomposed, and the effects of ultrasonic conditions (intensity and frequency) and reactor diameter on the PCE decomposition performance were investigated tinder a constant volume of liquid. The spatial distribution of PCE concentration in the reactor and the decomposition conversion were measured. The liquid mixing time was measured, and the reaction fields were visualized by using sonochemical luminescence. The spatial distribution of PCE concentration was relatively uniform for 100 and 200 kHz, while the PCE concentration was higher at the lower part of the reactor than at the upper part of the reactor for 500 and 800 kHz. Under the present range of ultrasonic frequency (100-800 kHz), the decomposition conversion increased with decreasing frequency. The reactor diameter was found to have an optimum value for the decomposition performance under the constant liquid volume.