A new photonic crystal fiber (PCF) with composite hexagonal air hole lattice is proposed and analyzed using the full-vector finite difference frequency domain (FDFD) method with anisotropic perfect match layer (APML) absorbing boundaries. We numerically demonstrate that the flattened dispersion of different levels, even the nearly zero ultra-flattened dispersion characteristics can be achieved through optimizing three geometrical parameters, two for air-hole diameters and one for hole pitch. As an example, the dispersion is 0±0.545 ps/(km·nm) from 1.48 μm to 1.78 μm wavelength when Λ, d1 and d2 are 2.1 μm, 0.5 μm, 0.8 μm respectively. The flattened dispersion feature makes it suitable for the wavelength-division multiplexing communication systems and nonlinear optics.