Abstract: Polarization properties of tapered fiber are discussed fiber are discussed in this paper.By the Maxwell equation and boundary condition,the field distribution of ideal fiber is analyzed and the transmission property of the fiber is also explained.Further more.geometric optics treatment is convenient due to the relation between the length of tapered fiber and its polarization property.Through the experments and analyses,we may draw the conclusion that the elliptic polarization light is obtained when linear polarization light transmits through the single mode fiber or after coupling.