Abstract：In the underground repositories，the microstructure change of surrounding rock under the action of the chemical corrosion will cause the increase of porosity in medium and the accelerative diffusion of chemical contaminator. Aiming to analyze the chemical corrosion effect on the environment medium，micro-local pattern and composition of sandstone specimens with size f50 mm×100 mm under chemical corrosion of NaOH solution with pH value of 12 and concentration of 0.01mol/L are tested using SEM and X-ray technology firstly. After a series of laboratory tests on evolution of porosity of sandstone specimens and pH value of solution at different periods under chemical corrosion of NaOH solution(0.01 mol/L，pH value is 12) are conducted；the microstructure change of sandstone under chemical corrosion is analyzed from the view of porosity change. On the basis of the results of tests and the theory of chemical thermodynamics，the corrosion mechanism is concluded for the dissolution of quartz matrix mineral and siliceous cement. Then，based on the theory of chemical kinetics，chemical thermodynamics，and solute transportation，a reactive-transport model for describing porosity change under chemical corrosion is established. Finally，a simplified mathematic model is derived to describe microstructure change of rock under chemical corrosion. And the numerical simulation is performed. The simulation result indicates that，with the corrosion time increasing，the porosity increases firstly and then is driven to stabilization in the end. The study results can be used as a valuable reference to understand the mechanism of the chemical corrosion effect on the microstructure change of rock damage evolution，to set up the corresponding damage constitutive model，and to offer an effective parameter for exactly estimating the safety and stability of many rock engineering projects such as dam foundation，radioactive waste repositories，slope and tunnel which are related to hydrochemistry.
