Abstract: To investigate the mechanism of sudden fault slip induced by working face mining in stepped fault within a workface, the study takes the WII02040501 working face of Tunbao Coal Mine, which includes 17 faults, as the background. Theoretical analysis and numerical simulation were employed to establish a theoretical model for fault slip-induced sudden instability and to study the catastrophe effect of mining-induced fault slip instability in this workface, with engineering validation conducted through field micro-seismic data. The results show that it is proposed that the evolution of combined fault normal and shear stress is the primary trigger for fault slip; the working face mining towards the stepped combined fault, both the shear stress and normal stress on the fault plane exhibit stepped changes, with the shear stress demonstrating higher sensitivity; during fault slip, the shear stress on the fault plane rapidly increases, and the ratio of shear stress to normal stress undergoes catastrophe effect, and the release and concentration of strain energy alternate in the mining area of the workface; when the working face mining to a distance of 40 m from the fault, the stepped combination fault initiated slip from the top and synergistically propagated downwards, leading to an overall sudden change and instability in the combined fault. Microseismic data indicates that when the workingface was approximately 80 meters away from the fault, the T7 combination fault began to activate, with an increase in the frequency and energy of micro seismic near the fault, aligning with numerical simulation results. After the working face passes through the fault 40 m, the microseismic frequency and energy reached their peak, indicating that damage and subsidence of the goaf roof, the fault experienced unloading effects, leading to a rapid decrease in normal stress, a rapid increase in shear stress, and overall fault sliding failure, consistent with the research findings.