Abstract: In International System of Units（SI），the plane angle is a derived Quantity，and its unit “Radian” is an auxiliary unit. But the plane angle is neither derived from the length base unit, nor traced to it, so the deriving relationship between the plane angle and the length basic unit could not be established. The plane angle has wide applications, important effects and unique performances, which is accordant with the demands of basic Unit. Therefore the suggestions are proposed for discussions as follows: the plane angle, “angle” for short, is a basic quantity; the unit of the plane angle“degree, angular minute and angular second”, is basic unit.

Key words: Plane angle, Angle, Basic unit, International System of Units（SI）, Discussion