For a round lattice micro-structure optical fiber, the birefringence properties are simulated by the finite difference beam propagation method. After analyzing the influence of different cross-section structure parameters on birefringence, we obtain an appropriate set of structure parameters. With these parameters, the polarization beat length remains stable in a wide wavelength range near the 1310 nm communication window, and the working bandwidth can reach 200 nm, so it has a better achromatic characteristic. The fiber is suitable for making wideband achromatic plate.