Characteristics of magneto-optic rotation crystal such as basic theories of magneto-optical ef. fect, the dichroism of magneto circulars, nonlinear of Faraday effect in magneto-optic crystal and magnetic clas.sification of material are analyzed. And common detection device for full-automatic polarization, such as step.ping motor which is used to control the analyzer rotation is introduced. Full-automatic polarization detection de.vices are difficult to reach higher accuracy due to the limitations of mechanical devices. Magneto-optic rotation crystal is suitable to be used in full-automatic polarization detection after the characteristic analysis. So a new scheme for full-automatic polarization detection devices by using magneto-optic rotation crystal is proposed.