To study the effect of acid gas and bending stress on the carbonation durability of highway tunnel lining， the accelerated carbonation test of concrete under the combined action of nitric acid erosion and bending stress was carried out， and the carbonation depth， carbonation substance content and microstructure of concrete were tested and analyzed. The results show that both nitric acid and bending stress can promote the carbonation of concrete. With the increase of nitric acid concentration and stress level， the carbonization depth increases and the content of carbonized substances decreases. Nitric acid erosion consumes alkaline substances and weakens the filling effect of CaCO₃ on pores， forms microcracks and increases porosity. The bending stress makes the microcracks develop further， form tensile cracks， and the microcracks are formed in coordination with carbonation.