Abstract: Cavitation characteristic of downstream pumping spiral groove seals were investigated experimentally based on a self-designed visualization experimental device and accurate measurement methods for film thickness and film temperature. Effects of rotating speed and oil pressure on the location of cavitation occurrence, cavitation distribution and cavitation boundary were discussed, and theoretical leakage and film thickness calculated respectively from Reynolds and JFO cavitation models were compared with corresponding test values. The results show that the cavitation of both the inner groove and middle groove type seals occurs in spiral grooves, but the cavitation shape is not the same with each other. For the two seals, the liquid film rupture boundaries all locate the helical boundary of back flow side as well as distinct liquid film reformation boundaries exist between the complete liquid film field and the cavitation field along the direction of increased circumference angle, relative to the liquid film rupture boundary. The increasing of oil pressure helps to inhibit the cavitation occurrence, while the increasing of rotating speed is opposite. Especially for the inner groove type seals, effect of oil pressure is more obvious on the cavitation occurrence. Both Reynolds and JFO cavitation models can be used to accurately predict the leakage and film thickness under the situation of lower rotating speed or higher oil pressure, namely, without cavitation or smaller cavitation area. While JFO cavitation model can be more suitable to predict the parameters than Reynolds cavitation model by which the values predicted are rather large under the circumstance of higher rotating speed or lower oil pressure, with larger cavitation area.