Abstract: To explore the effect of maximum principal stress near fault on fault activation instability, this paper takes KF₇₆ fault of Jisan Mine as the engineering background, uses FLAC^3D software to build a numerical analysis model to carry out the excavation simulation on the upper and lower plates of the fault respectively and analyze the changes in the direction and magnitude of the maximum principal stress near the fault with the advance of the working surface. Research shows that: the trend of fault activation increases with the advancing of working face, when the footwall is excavated, the working face is 40 m away from the fault, the fault is active; the maximum principal stress deflection and concentration near the fault are intensified and the range is enlarged with the advancing of working face towards the fault; compared with the hanging wall of the fault, in the foot wall mining, the maximum principal stress deflection and concentration are more apparent, the influence range is larger, and the activation of the fault is more likely to occur by the mining of the foot wall.