The influence of different chemical environments on the deformation characteristics of red sandstone was investigated by combining uniaxial compression tests with digital image correlation (DIC) technology. The evolution of surface strain fields of red sandstone under acidic, neutral and alkaline conditions was systematically examined. On the basis that the microelement strength of rock follows a log-normal distribution, the effects of the mean strength and dispersion of microelement strength on deformation characteristics were further analyzed. By incorporating the Drucker-Prager (D-P) strength failure criterion, a chemical damage constitutive model based on strain non-uniformity was established. The results show that, during uniaxial compression, strain localization of specimens in a neutral environment mainly occurs in the end regions, whereas in acidic and alkaline environments, strain localization appears not only at the ends but also in the middle region. With increasing acidity or alkalinity of the solution, strain localization is initiated at an earlier stage. This behavior is attributed to the alteration of the internal microstructure of the rock by acidic and alkaline corrosion, which leads to a decrease in the microelement mean strength and an increase in the dispersion of strength distribution, thereby accelerating the accumulation of local damage. By introducing a chemical damage variable and considering the influence of the chemical environment on rock microelements, the proposed damage constitutive model can accurately predict the stress-strain behavior of red sandstone, providing new theoretical support for understanding deformation mechanisms and engineering applications of rocks in complex chemical environments.