Abstract: In order to study the deterioration mechanism of concrete durability under complex multi-factor condi? tions, relying on a major tunnel project case in the alpine region and considering the interaction of multiple factors,the accelerated laboratory test method is used to study and analyze the influence of salt intrusion, freeze-thaw cycles, carbonization alternation and their coupling effects on concrete durability based on orthogonal tests. The freeze-thaw damage, composite salt erosion, strength failure and carbonization erosion caused by different environments are analyzed to reveal the complex coupling conditions and the synergistic effects of additives and admixtures on the deterioration of concrete durability. The results show that the alternating cycle of salt intrusion, freeze-thaw and carbonization can temporarily reduce the capillary porosity of concrete, and this alternating cycle case will cause a greater loss of compressive strength, and the combined salt erosion has a certain degree of inhibition on the carbonization depth of concrete. The influence of fly ash content between 10% and 20% and air entraining agent content between 0.8% and 1.2% on concrete durability is relatively stable.