The optical performance of the fused-taper fiber device is determined by microstructure and morphology of the fused taper region, which are determined by technological conditions. In order to find out the effect of technological conditions on microstructure and morphology, experiment has been carried out. Taking the couplers manufactured at different drawing velocities as samples, the wave number of the fused regions and taper regions is measured with micro infrared spectrometer, and the morphology of the same point is recorded with scanning electron microscope (SEM). It is discovered that there are two characteristic peaks: one is at about 1100 cm-1, the other at about 810 cm-1. The wave number of the former peak is highest at the taper region, the one at the fused region followed, and the one of bare fiber lowest. The 1100 cm-1 characteristic peak shifts to higher wave number while the drawing velocity increases. In the taper region, cracks are discovered. And the cracks are more obvious while drawing velocity increases. In the fused region, there appear crystallines on the surface of the coupler, and the crystalline grain becomes smaller while the drawing velocity increases. A higher quality of coupler cannot be obtained until less change of the microstructure and less defects under the proper drawing velocity (here is 150 μｍ/s) are realized.