Abstract: Influencing factors are analyzed on the diameter variation and distribution of bigger oil mist particles flowing through a annular clearance. The results show that: when the clearance length is 20 mm, the bigger oil mist particles condense after flowing through the clearance, and the average size of the condensed oil mist particles decreases gradually with the increasing of the oil mist inlet pressure, intake pressure, radial clearance and air flow; when the clearance length is 60 mm, most of the bigger oil mist particles condense in the clearance, and the condensation efficiency increases gradually with the increasing of air flow; when air flow is constant, the condensation efficiency decreases with the increasing of the radial clearance.