Abstract: 50D hollow polyester filaments were used to be embedded the composite materials simulating the porosity of the composites, which was used as standard test blocks. Carbon fiber reinforced epoxy resin composites were prepared with three kinds of thicknesses(1.5, 3.0 and 5.0 mm) and five kinds of void contents (0-5.76%). Ultrasonic C-scan was adopted to measure the ultrasonic attenuation of the composites with different void contents. Testing results were compared with the results using Boeing Co.'s standard test block. The effect of arrangement density and position of polyester filament on ultrasonic attenuation of the composites were studied. The results show that there is a good consistency between the standard test block made in this paper and Boeing Co. standard test block, and using hollow polyester filament is feasible to simulate the porosity of composites. The void content and ultrasonic attenuation increase with the arrangement density. The ultrasonic attenuation keeps stable when the position of polyester filament in thickness direction changes.