Abstract: As one of the main pavement materials, asphalt concrete is inevitably exposed to freezing and thawing damage. Through CT scanning of asphalt concrete specimens undergoing different freeze-thaw cycles, and using digital image processing technology to process and analyze CT gray images, the internal freeze-thaw damage can be obtained. The geometric characteristics of internal crack propagation under freeze-thaw cycle were quantified based on fractal theory. Fracture toughness of asphalt concrete after freeze-thaw cycle is considered as the key index to demontrate the damage degree of its mechanical properties. The critical crack stress, stress intensity factor and fracture toughness equation considering fractal characteristics are established. The results show that the average fractal dimension reflects the fluctuation characteristics of freeze-thaw cycle. Fracture toughness is determined by crack geometry parameters. The mechanical parameters such as elastic modulus, critical cracking stress and fracture toughness gradually decrease with the increase of the number of freeze-thaw cycles.