Abstract: A mesoscale model of void-containing composites was built by DIGIMAT/FE, which includes three phases (fiber, resin and void) and effectively reflects the real microstructure and mesoscale material properties of the composites. Ultrasonic excitation was loaded into the model by ABAQUS/EXPLICIT for finite element analysis (FEA). Acoustic propagation process was extracted to build a relationship between ultrasonic attenuation coefficient and porosity of unidirectional continuous fiber reinforced composites. Taking T800/epoxy composite as an example, the effect of void size on the numerical prediction of ultrasonic attenuation was studied, and the accuracy of the FEA model was verified by making a comparison between the numerical and analytical predictions. The simulation method will be an effective guidance for experimental process, and a theoretical basis for reducing porosity to increase the service performance of composites.