Germanium doping in silica can enhance the effective nonlinear index of refraction,since it is not equal for GeO2 and SiO2. Properties of enhanced nonlinearity,effective mode area,and chromatic dispersion in microstructure fiber (MF) with a GeO2-doped core are theoretically investigated by using an all-vector finite element method. With little difference in mode field distribution compared to the pure silica situation,the nonlinearity of PCF is greatly enhanced by doping Ge in the core region. Further more,the effect of doping concentration and radius of doped area on fiber′s nonlinearity is studied.