The optics principle and functions of fused polarization-maintaining fiber coupler is determined by propagation properties. In order to investigate the effects of parameters, based on the theory of thermal-structural-electromagnetic multiphysics field interaction, the biconical models of the fused PANDA fiber coupler were given. Using finite element method the effects of the propagation properties for fused PANDA fiber coupler is analyzed. The results show that longitudinal electromagnetic field distribution is influenced by the refractive index difference between the stress applying part (SAP) and cladding, the distortion of distribution is increase with the D-valve. The propagation constants for HEx11 and HEy11 modes are insensitive to the angle disparity of the birefringent axes, and they affect to the extinction ratio directly by coupling coefficient. The propagation constants for HEx11 mode is sensitive to the ellipticity of fused taper section, the change of Δβx11 is 0.14% when the ellipticity fusion is increased 6.67%, and the numerical results show that it can get high performance when the ellipticity of fused taper section is 0.56.