A new structure of single polarization single mode (SPSM) microstructured polymer optical fiber (mPOF) is proposed and numerically analyzed by using a full vector finite element method with anisotropic perfectly matched layers. The cutoff wavelength of two linearly polarized states can be design by varying the structure parameters of mPOF. The confinement loss are also numerically calculated and optimized at communication wavelength of polymer optical fiber (POF) of 650 nm. From the numerical results it is confirmed that the proposed fiber is low-loss SPSM mPOF within the wavelengths ranging from 0.63 μm to 0.73 μm, where only the slow-axis mode exists and the confinement loss is less than 0.05 dB/m.