Abstract: The West Sichuan tectonic belt,located in the eastern part of the Qinghai-Tibet Plateau,harbors high-temperature geothermal resources and experiences frequent seismic activities. To investigate the corrosion damage caused by geothermal fluids to fault rocks,this paper conducted water-rock interaction experiments under subcritical water environments(100~374℃,saturated vapor pressure 0.1~22.1MPa) at 100~350℃ on mylonite from the Jinhe-Qinghe fault in western Sichuan. The variation of solution composition and rock pore structure with temperature was analyzed by Inductively Coupled Plasma Mass Spectrometry(ICP-MS) and Low Temperature Nitrogen Adsorption(LTNA)experiments. The results demonstrated that the dissolution rate of Si in western Sichuan mylonite was positively correlated with the water-rock reaction temperature in the range of 100~350℃,and the dissolution rate at 350℃was 11.97 times higher than that at 100℃,while the dissolution rate of Na,Ca,K,Al,Mg,and other metal elements was much lower than that of Si. Under long-term hydrothermal corrosion,a large amount of Si in mylonite and the disintegration of silicate minerals will destroy the pore structure of the rock. With the initiation and development of micropores and mesopores,the total pore volume of mylonite increased from 0.00541cm³ ·g^-1 at 25℃to 0.00659cm³ ·g^-1 at 350℃. The specific surface area increased with the heat treatment temperature,which will enhance the contact between water and mylonite,resulting in further deterioration of the rock. This study provides insights into the mechanism of hydrothermal corrosion of mylonite in subcritical water environments and the influence of geothermal fluids on fault stability.