Fused planar 3×3 single mode fiber coupler is very important in optic switch, optic buffer, optic resonator and optic filter etc, both the evolution of polarization and the performance of wavelength are the crux. Based on the coupled-mode equations, the theoretical analysis of a fused planar 3×3 fiber coupler was presented. It is not coupling field but optic fiber pigtail operating on the evolution of polarization. The appropriate distance of the cores of the fiber (it is 12.5 μm to us) is obtained via analyzing the relation between the spliting ratio and wavelength. And the fused planar 3×3 single mode fiber coupler is fabricated which has long coupling field by moving flame. The experiment results indicate that the splitting ratio of output of coupler has little change when the wavelength of the input optic range from 1.500 tp 1.575 μm, the experiment results are in good agreement with the theoretical analysis.