Abstract: For applying Φ10 mm centrifugal extractor to study on the back-extraction section of plutonium purification cycle in Purex process, the characteristics such as the entrainment state of the two-phase exit liquid, the volume of the liquid in both the annular space and the rotor were studied when the rotor speed was changed, with the two-phase flow ratio (A∶O) 1∶4 and the heavy phase weir diameter 6.4 mm, 6.6 mm and 6.8 mm, respectively. The results show that the centrifugal extractor has a stable operational state when the total flow is less than 9.0 mL/min and the rotor speed is greater than 4 000 r/min. There is no entrainment in the liquid two-phase exit. The liquid-volumes in the annular space and the rotor are about 0.7 mL and 2.2 mL, respectively. The contact time of two-phase can be calculated by relating the total flow.