The properties of tapered fiber’s tapered region are studied. The transmission and coup ling properties of tapered fiber are relative to the structure of tapered region. Therefore, both transmission and coup ling efficiencies can be improved through improving the shape of tapered region. Meaningwhile, the polarization andmodulating properties of tapered fiber are analyzed. L inearly polarized light turns into ellip tical polarized light after transmitting through tapered fiber, but itsmodulating p roperties keep the same.