Abstract: When ultrasonic propagates in porous composites, the interaction between ultrasonic scattering waves near voids and the scattering attenuation mechanism have not been clarified. Aiming at these problems, utilizing the finite difference time domain method, the ultrasonic propagation in carbon fiber reinforced plastic (CFRP) with the porosity of 7.47% was numerically calculated. The ultrasonic scattering attenuation coefficients of both 2D real morphology voids and spherical voids with different size ranges in CFRP laminates were studied contrastively. The results show that, for the small voids with the horizontal size m≤λ/8 and the median voids with λ/8_s of the spherical voids is generally less than that of real morphology voids. When the horizontal size of voids is m<2λ/3, the large size voids and slender voids could enhance ultrasonic scattering attenuation on the whole.