Four kinds of microstructured polymer optical fibers based on Topas cyclic olefin copolymer(COC) are designed.The effective index of the fundamental mode,the mode area and the numerical aperture are calculated by using the finite element method.Effects of structure parameters upon the mode field distribution,single mode property and dispersion property are discussed.Structure parameters corresponding to very large or very small effective mode area,endless single mode operation and flattened-near-zero dispersion are obtained.These fibers have larger numerical apertures compared with silica or PMMA based ones,and display flattened-near-zero dispersion.