Abstract: The problem of the angle of incidence on the surface of a monopodium whose optical axis is discretional （Brewster＇s angle） is studied when the reflected rays is totally perpendicular to the plane of incidence. The Brewster angle is analysed when optical axis is discretional, then the paper gives the conclusion is obtained when optical axis is perpendicular to the plane of incidence by using a set of simple calculating method, the incorrectness of some papers is pointed out

Key words: monopodium, Brewster angle, direction of optical axis, reflectance