This paper describes a new type of optical system in optical head for magneto-optic disk drive, expounds theoretical the basic principle for magneto-optio information read out. The system has improved the performonoe of optical system reduced optical noise, incrased efficiency of optical energy. It has been applied to the development for a prototype magneto-optio disk(51/4inches) drive and the ratio of read out signed-to-noise has been reached more them 50 dB.