Experiments of ultrasonic polishing the 45# steel shaft without abrasive are carried out by using orthogonal test method to study the polished surface roughness, and experimental results are analyzed with range method. The influence of polishing parameters on the polished surface roughness could be arranged as follows: feed rate, power of generator, preload pressure and radius of the tool head, in which the feed rate brings the most remarkable influence on the polished surface roughness. The surface roughness value reduces at first and then increases when the radius of tool head, preload pressure and power of the generator increase. The surface roughness value increases with the feed rate. Comparative experimental results of ultrasonic polishing without abrasive and the conventional rolling indicate that lower surface roughness value may be obtained by ultrasonic polishing without abrasive.