To study the relationship between the microstructure and the macroscopic mechanical parameters of the acid-corroded sandstone, the mechanical parameters of sandstone corroded by hydrochloric acid were examined based on the physical property testing and the uniaxial mechanical testing. The characteristic parameters and the fractal dimension of the pore structure were obtained via SEM-EDS. The chemical damage variable based on porosity was established and the constitutive model of the corroded sandstone was derived based on the extended Lemaitre strain equivalence principle.The results show that the mass loss of sandstone immersed in hydrochloric acid at pH=1, 3 and distilled water with pH=7 for 180 days increased by 1.22%, 1.08%, and 0.57%, respectively.The uniaxial compressive strength decreased by 51.93%, 41.91%, and 27.11%, respectively. It has obvious tempo effect. The average pore size and the fractal dimension of pores of the acid corroded sandstone increase with the corrosion time; The macroscopic mechanical parameter deterioration degree of sandstone iscorrelated with the mass loss rate and the microscopic porosity of sandstone. The Feasibility of the proposed model is validated via the numerical and laboratory testing results.