Abstract: This paper studies the modulation of the amplitude modulating nonlinear medium defects on a Gaussian beam. Based on the Fresnel diffraction integral and Taylor series expansion, the model of the beam propagating through the nonlinear medium with defects is built, and the analytical expressions for the intensity distribution at different distance of a Gaussian beam getting through the defective nonlinear medium are derived. The impact of the defect size and the additional phase shift in the medium on the intensity distribution of the beam propagating through the medium is studied. It is shown that larger defects and more additional phase shift lead to deeper beam modulation. Under the modulation of the defects and the nonlinear effect in the medium, there would be a maximum intensity near the rear surface of the nonlinear medium before the beam convergence or diffusion, when the medium has positive or negative nonlinear index of refraction, and the larger the phase shift of the beam isin the medium, the stronger the maximum intensity becomes.