Cutoff wavelength is an important parameter for optical fiber. The cutoff properties of hole-assisted optical fibers that comprise six air holes in cladding are investigated by a full vector orthogonal function model. It is shown that when the material dispersion is neglected, the effective cladding index is a function of wavelength due to the introduction of air hole into the cladding of fiber; the effective cladding index is determined by the relative air hole size in cladding, and independent of the relative index difference of doped core. The fundamental mode cutoff occurs only if d/Λ is large enough, which is similar to the case of traditional W-shaped refractive index fibers. The cutoff wavelength of each mode decreases as the relative air hole size d/Λ increases from 0.2 to 0.9; the slope of cutoff wavelength versus d/Λ curve decreases as the order of mode increases.