<p>The rising frequency of injection-induced seismicity necessitates a deeper understanding of the fluid-fault interaction mechanisms for improved prediction and mitigation of seismic hazards. In this study, triaxial loading tests were conducted on granite specimens under constant axial (<i>σ</i>₁=12&#xa0;MPa) and confining stresses (<i>σ</i>₃=5&#xa0;MPa), with the dynamic behavior of fractures being analyzed during fluid injection. The experimental results demonstrate that the H₂O and CO₂ injections both induce a notable increase in the friction coefficient. However, compared with the H₂O injection, the CO₂ injection results in a more significant stress drop across the fracture surface. Subsequently, building upon the existing experimental findings, a numerical model employing a spring-slider system that incorporates inertia effects was developed to investigate the mechanism of fracture instability induced by fluid injection. Finally, based on this numerical model, the influence of various friction parameters and different injection schemes on the sliding behavior was further discussed.</p>