Transmission properties of the pulled and the etched fiber tapers have been analyzed with local couple mode theory. To decrease the mode coupling loss and increase the focusing effect, the characteristic transition points are introduced.For taper pulled fiber, the optimal fabrication position of fiber microlens is near the characteristic transition point, while for the taper etched fiber, the optimal fabrication position is between the taper tip and the characteristic transition point.The focusing property of Gaussial beam through fiber microlens for trapping of particles is also discussed.