The single-polarization single-mode (SPSM) micro-structured polymer optical fiber (MPOF) was designed based on polymethyl methacrylate (PMMA). A full vector plane wave expansion method together with perfectly matched boundary conditions is adopted to study the SPSM properties. The dependence of SPSM bandwidth and operation wavelength on fiber parameters was investigated numerically. It indicates that only one polarization state of the fundamental mode can be transmitted within the visible light region from 0.57 μm to 0.71 μm according to the different cutoff wavelength for two orthogonal polarization modes. Moreover, the confinement loss of guiding mode is investigated using the beam propagation method. For MPOF with only 7 rings of holes, the confinement loss less than 1.24 dB/m is obtained at the 0.65 μm. This low loss SPSM-MPOF can greatly eliminate the polarization crosstalk and polarization mode dispersion.