Subway concrete is easy to be attacked by aggressive CO₂ in underground space, and alkali aggregate reaction (AAR) is a severe durability problem which is difficult to find and repair. Durability decrease of subway concrete caused by these two problems seriously affects the normal use of the subway tunnel. To investigate the impact of nano-particles on the durability of subway concrete under the combined action of aggressive CO₂ and AAR, two kinds of nano-particles (nano-SiO₂ and nano-Fe₂O₃) were respectively mixed into plain concrete to prepare concrete with nano-particles. Durability test was carried out by using a self-developed equipment, and erosion depth, expansion, and sonic velocity were selected as indices to evaluate the durability of the concrete with nano-particles under the combined action of aggressive CO₂ and AAR. Test results show that after mixed with nano-particles, the erosion depth and expansion of the concrete were decreased obviously, while the sonic velocity was increased significantly, which demonstrates that the durability of the concrete with nano-particles was better than that of plain concrete. At the age of 182 d, the concrete with 2% of nano-SiO₂ showed the best durability performance that the erosion depth and expansion were the smallest and the sonic velocity was the largest with least decrease, followed by the concrete with 1% of nano-Fe₂O₃. The enhancement of durability was due to the special physical and chemical properties of the nano-particles which improved the microstructure of the concrete and the chemical composition in pore solution.