A new method of optical control is put forward based on conical effect in biaxial crystal.When the incident light spread along optical axis direction,the propagation direction will change with the polarization direction.By controlling the magnetic field on the magneto-optic modulator,the polarization direction can be changed,thus the laser beam direction control is realized.The fundamental of disk tracking is analyzed and overall plan is also designed,the relationship between polarizing angle and tracking displacement is obtained by numerical simulations,so this plan is reasonable.Compared with traditional tracking means of machine -electricity,this kind of plan has the following advantages:light weight,small volume and fast transient response.A new method for optical switch and scanning is provided meanwhile.