The structure of microstructured optical fiber (MOFs) has a strong impact on its nonlinearity parameter and therefore, could be designed to meet the needs of optical processing applications. By a full-vector finite element method, the nonlinearity coefficient of MOFs with a silica core and two kinds of air hole cladding structures, i.e., the hexagonal lattice and square lattice, is computed respectively. The dependence of the nonlinearity coefficient of MOFs on the structure parameters and the wavelength is analyzed. The results show that, for a given wavelength and a given air-filling fraction, the nonlearity coefficient has a maximum when the pitch of air holes changes, if the air holes are very large, nonlearity coefficient maximum of the hexagonal lattice and the square lattice amount to approximately 77w-1km-1 and 54w-1km-1 respectively; for a given wavelength and a given pitch of air holes, the nonlinearity coefficient increases when cladding air-filling fraction increases; for given structure parameters, the nonlinearity coefficient decreases while the wavelengh increases. The above results are the good reference to investigation and use of the MOFs.