Abstract: Limestone-concrete composites are widely found in engineering structures in southwest China, yet they are highly susceptible to degradation under acid-rain exposure, posing significant safety risks. To investigate the mechanical properties and macroscopic failure characteristics of such composites under varying degrees of acidic corrosion, conventional triaxial compression tests were conducted following corrosion in solutions with pH values of 3, 5, and 7. The numerical simulation test of plastic deformation propagation during loading was carried out by FLAC^3D, and the accuracy of the numerical simulation results was verified by the energy evolution characteristics. The results show that when the pH value decreases from 7 to 5, the change amplitude of the peak stress, peak strain, and elastic modulus of the composite is greater than that when the pH value decreases from 5 to 3, showing a trend of the weakening rate of the mechanical performance of the combined body with the decrease of pH value. The distribution of the plastic zone simulated by FLAC^3D is consistent with the crack distribution after loading of the actual assembly, and the main failure mode is the penetrating tensile and shear composite failure at an angle of 45°, which gradually transitions to pure shear failure as the corrosion solution becomes more acidic. Numerical simulations show that the concrete component first produces plastic deformation when loaded to 0.7σ_c, expands with the loading process, and extends to the limestone component, resulting in the failure of the specimen. The results show that the mechanical properties of the composite deteriorate significantly after acid corrosion, and begin to fail after being loaded to 0.7σ_c. Therefore, the load of the combination should be controlled within 0.7σ_c in the design of the limestone underground engineering in the southwest acid rain area, which provides an important scientific basis for the prevention and control of engineering disasters.