The unavoidable defects exists in the optical component will modulate the phase and the amplitude of the beam propagate in the system. Based on the Fresnel diffraction integral, the propagation mode of the Gaussian beam modulated by the local phase is built and the analytical expressions for the intensity distribution and angular spectrum of a Gaussian beam modulated by finite phase modulated defects has been derived. The impact of the modulation depth and the size of the defects on the intensity distribution and angular spectrum of the beam modulated by phase modulated defects is studied. It shows that in the process of transmission the evolution of the light intensity is the same for different modulation depths and sizes of the defects. The deeper of the modulation depth of defects that modulated the beam, the higher of the intensity produced along the propagation process. The larger of the defect, the nearer of the proposition where produced the highest intensity from the defects location. The angular spectrum in the low frequency area become smaller and the angular spectrum in the high frequency area become greater with the increase of modulation depth and the size of the defect as well as the defect getting closer to the middle of the beam.