Abstract: The presence of pores in composites results in a decrease of material properties, therefore, it is critical to the detection of material pores. Carbon fiber (CF) cloth/epoxy resin laminated plates with different number of layers and different porosities were prepared by using different amounts of isopropanol(IPA). The ultrasonic attenuation coefficient of the test piece was calculated by pulse reflection method. The distribution, shape and size of the pore were characterized by metallographic microscopic analysis. The porosity of the test piece was obtained by analyzing the metallographic micrograph by MATLAB. The effects of porosity on the sound velocity, sound impedance and ultrasonic attenuation coefficient of the CF/epoxy resin laminated plates were discussed, and the fitting formulas of porosity, material layer number and ultrasonic attenuation were given based on the experimental data of porosity and ultrasonic attenuation of four samples with different layers. The results show that as the amount of IPA increases, the porosity of the laminate (2 mm) increases from 1.09% to 4.16%, the sound velocity and acoustic impedance of the material decrease, and the ultrasonic attenuation coefficient increases from 2.51 dB/mm to 5.34 dB/mm. When the porosity is 1%, the thickness increases from 2 mm (8 layers) to 5 mm (20 layers), and the attenuation coefficient increases by 0.54 dB/mm.