The apparent morphology， mass loss rate， relative dynamic elastic modulus， compressive strength and pore structure of blue bricks after freeze-thaw cycle were studied. The relationship between fractal dimension and compressive strength， porosity and frost resistance was established based on fractal theory. The results show that with the increase of freeze-thaw cycles， the small pores on the surface of the blue brick deteriorate into large pores and gradually extend into cracks， resulting in an increase in the mass loss rate， and a decrease in the relative dynamic elastic modulus and compressive strength. After freeze-thaw cycle， the internal pores of the blue brick have obvious fractal characteristics， and the fractal dimension is distributed between 2.964 2 and 2.982 7. The fractal dimension of blue brick after freeze-thaw cycle is positively correlated to compressive strength and negatively correlated to porosity， and its fractal dimension is also highly correlated with frost resistance. The fractal dimension can be used to evaluate the microscopic pore structure change of the blue brick， and can also reflect the influence of the complexity of the pore structure on the macroscopic properties of the blue brick after freeze-thaw cycle. The research results provide a basis for the protection and durability damage of ancient architectural blue bricks in cold regions.