By using the multiple-carrier model and uniaxial symmetry and photoinduced mechanisms, the relationships of electrooptic coefficient γ with the distance d of D-fiber, poling time t and applied voltage V in the silica fiber after the thermal/electric-field poling (TEFP) are theoretically calculated. The results show that if d is short enough and poling time is suitable, the electrooptic coefficient can effectively be increased; the electrooptic coefficient is approximately proportional to the square-root of the applied dc voltage. The ratio of γ33/γ13 approaches to 3. The theoretical results are well consistent with experimental reports.