Turbine is a common mechanical structure in drilling industry, which is usually used in downhole turbogenerator, turbodrill and so on. With the continuous development and innovation of computational fluid dynamics (CFD) theory and numerical methods, CFD method has been become an important means for the study of downhole turbine performance. At present, the research on downhole turbines is static. In this paper, using FLUENT software and sliding mesh method, UDF file is compiled to simulate the dynamic performance of downhole turbine. The effects of external load, number of blades, flow rate and blade installation angle on the hydrodynamic performance of downhole turbine are studied, and the start-up characteristics and movement process of downhole turbine are analyzed. The results show that when the start-up moment is less than the load, the turbine is stationary; when the start-up moment is greater than the load, the turbine starts to rotate. In the process of the turbine’s rotation, the force moment of the turbine decreases, while the speed and impact force increase continuously. When the rotational velocity is stable, the torque produced by the fluid is balanced with the load, and the impact force is stable.