More detailed and accurate modeling is very important for analyzing and optimizing the tribological performance of the piston-ring-cylinder liner system. However, due to the difficulty of modeling and solving, theoretical studies on the three-dimensional (3D) tribodynamics of piston rings are limited. The tribodynamic model which couples the dynamics, mixed lubrication, and blow-by of piston-ring pack assemblies has not been found yet. Therefore, in this study, a 3D tribodynamic model of the piston-ring pack is developed considering the influence of piston secondary motion and the interaction forces and moments between piston ring and cylinder liner as well as between piston ring and ring groove. In addition to the ring end gaps, the influence of ring dynamics is also contained in the blow-by model. Coupled with gas flows and piston rotation, ring motions in the ring groove are investigated. It is found that ring dynamics has significant effects on the tribological performance, the axial reversing movement of piston ring is the main cause of gas pressure oscillation, piston motion has an obvious influence on the ring dynamics, the interaction forces and moments between piston and rings increase the secondary motion amplitude of piston, especially near the fire top dead center.