Due to the recycling of construction waste, recycled concrete has gradually become a viable material in the construction industry. To study the strength property of the recycled concrete after freeze-thawing experiments, recycled concrete and ordinary concrete were tested for their post-test strength after freeze-thawing for 0, 50, and 100 times. The result shows that the strength of the recycled concrete declined more quickly than that of normal concrete after freeze-thawing. In the paper, the two kinds of concrete underwent permeability test and the two kinds of aggregate underwent mercury intrusion. After the comparison of the inner structure of the concrete and aggregate was obtained, the influence of concrete pore structure on strength after freeze-thawing was further analyzed. The result of the permeability test shows that the porosity of recycled concrete is large when taken as a whole, and the water content is higher after steeping, which reduces the strength of the material. Mercury intrusion results also show that the pore structure of recycled aggregate is poor and that there are more internal micro-cracks. Therefore, in areas with regular freeze-thawing cycles, particularly in humid areas, the use of recycled concrete should be prudently used and handled accordingly.