The local mode-coupled model is used to analyze theoretically the light field property of fiber taper in scanning near-field optical microscopy. Differential equations of the forward and backward fundamental mode fields in fiber taper are given. The backward coupling coefficient of fundamental mode is obtained numerically, and it can reach about 1% at most. The reflection makes the fiber taper act as an output mirror of tapered fiber laser resonator. It is also shown that the parabolic taper has a lower reflected coupling coefficient than the truncated taper. the experimental results of the reflection wave from fiber probe are given.