Abstract: The exploitation of shale oil and gas is of great significance for increasing the proportion of clean energy consumption and achieving carbon reduction targets. During the development process, the effective stress acting on faults is reduced due to pressurized fluid injection, which can lead to frictional instability and fault slip. In this paper, the frictional behavior of faults in shale reservoirs is studied through fault slip experiments. A cylindrical shale specimen with a prefabricated fault was placed in a triaxial compression chamber to simulate in-situ reservoir stress, and fault friction instability was induced via fluid injection through a borehole. The dynamic changes in stress, slip displacement, and friction coefficient during fault instability and slip were monitored. The results show that fluid injection in shale reservoirs can trigger fault instability and shear displacement exhibiting stick-slip behavior, and that the frictional evolution during fault slip directly influences slip characteristics. After the onset of slip, an initial phase of slow slip is observed, followed by a decrease in the friction coefficient and an increase in the slip rate. Unstable slip with significant shear displacement occurs during the late stage of fault slip. The fluid pressurization rate exerts a controlling influence on the slip behavior of fracture surfaces in shale reservoirs. A higher fluid pressurization rate leads to a more unstable slip process, with significantly increased slip rate and cumulative slip, which may result in more severe abrupt changes and impact subsequent production operations.