In order to explore the dynamic characteristics of the mechanical seal under different fault degrees, this paper selected the upstream pumping mechanical seal as the object of study. The research established the rotating ring-fluid film-stationary ring 3D model, which was built to analyze the fault mechanism. To study extrusion fault mechanism and characteristics, different dynamic parameters were used in the analysis process. Theoretical analysis, numerical simulation, and comparison were conducted to study the relationship between the fault degree and dynamic characteristics. It is the first time to research the dynamic characteristics of mechanical seals in the specific extrusion fault. This paper proved feasibility and effectiveness of the new analysis method. The fluid film thickness and dynamic characteristics could reflect the degree of the extrusion fault. Results show that the fluid film pressure fluctuation tends to be more intensive under the serious extrusion fault condition. The extrusion fault is more likely to occur when the fluid film thickness is too large or too small. Results illustrate the opening force is affected with the fluid film lubrication status and seal extrusion fault degrees. The fluid film stiffness would not always increase with the rotating speed growth. The seal fault would occur with the increasing of rotating speeds, and the leakage growth fluctuations could reflect the fault degree.