Abstract: In the developing process of ion beam polishing equipment, the choice of scanning mode of ion source is very important. Traditional scanning process has two different ways. One is the mode of rectangular coordinates and the other is the mode of polar coordinates. According to the features of rectangular coordinate system and polar coordinate system, ion beam polishing with scanning mode of rectangular coordinates can be implemented in polar coordinates system. This method takes dwell time algorithm in rectangular scanning mode, which is much more simple. And in the same circumstances, its machinable round mirror caliber in polar scanning mode is bigger than that in rectangular scanning mode. Movable area of ion source in the way of polar coordinates is a line. Its rest place can be put other things, so dimensional utilization rate is higher. According to the simulation analysis of this new method, its feasibility has been proved.