To investigate the effects of hydrochemical corrosion and engineering disturbances on the physical and mechanical properties of soft red-bed rock in South China, H₂SO₄solutions with pH values of 4 and 6 were used to simulate acidic environments, NaOH solutions with pH values of 8 and 10 to simulate alkaline environments, and a Na₂SO₄ solution with a pH of 7 to simulate a neutral environment. Triaxial compression tests were conducted on corroded samples to analyze the deterioration patterns of mechanical parameters. Scanning electron microscopy (SEM) was employed to analyze the microstructural changes in the corroded rock. Based on the Drucker-Prager criterion, a damage constitutive model for red-bed soft rock was established by introducing a chemical damage variable and a Weibull distribution function, considering damage thresholds. The results indicate that the physical and mechanical properties of the rock deteriorate significantly after corrosion. When the pH decreases from 7 to 4, the peak strength drops by 28.1%, and the elastic modulus decreases by 16.38%. When the pH increases from 7 to 10, the peak strength drops by 15.84%, and the elastic modulus decreases by 10.11%. The increase in the concentration of acid and alkali in the solution will both cause the expansion of internal fractures in red-layer soft rock and disrupt the continuity of the skeletal rock framework structure. The influence of solutions with different pH values on mechanical parameters is in the following order: strong acid (pH = 4) > strong base (pH = 10) > weak acid(pH = 6) > weak base (pH = 8) > neutral (pH = 7). The model calculation results fit well with the test data, which can provide a theoretical basis for engineering construction in South China.