<p>The deterioration of coal’s mechanical properties following hydraulic fracturing for permeability enhancement can lead to a decrease in coal reservoir permeability, affecting the stability of coalbed methane extraction. Therefore, it is essential to investigate the mechanical behavior of coal after reservoir fracturing. This study investigates the strength, deformation, and failure characteristics of deep coal through true triaxial compression tests under high-stress thermo-hydro-mechanical-chemical coupling conditions. The results indicate that the treatment of viscoelastic surfactant fracturing fluid (VES-FF) increased the internal friction angle of coal samples by 5.53%, decreased cohesion by 50.09%, and reduced compressive strength by 56%. The degradation effect of VES-FF causes coal to exhibit ductile failure characteristics under low-temperature and low-gas-pressure conditions. With increasing gas pressure and temperature, the ductile failure behavior becomes more pronounced, peak strength decreases, and peak strain increases. Elevated temperature and gas pressure enhance the strength deterioration induced by VES-FF, leading to greater coal deformation, whereas the lateral expansion coefficient shows an opposite trend. Under true triaxial compression, all coal samples exhibited single-slope shear failure with a failure angle of approximately 60°. The degradation caused by VES-FF increases the number of secondary cracks during coal deformation and failure, a trend that intensifies with rising gas pressure but diminishes with increasing temperature. When temperature reaches 70&#xa0;°C, it becomes the dominant factor controlling the strength, deformation, and failure characteristics of deep coal. This research provides theoretical guidance for optimizing hydraulic fracturing and permeability enhancement technologies in deep coal reservoirs.</p>