Background/Introduction <p>Two-stage gear transmission systems are critical for power transfer in high-torque applications, but long-term heavy-load operation often leads to concurrent gear and bearing faults. Existing research focuses more on single faults, leaving multi-component coupling fault analysis insufficient.</p> Purpose <p>This study aims to explore the vibration characteristics and coupling mechanisms of gear tooth pitting and bearing raceway spalling, providing theoretical support for accurate fault diagnosis and operational safety protection.</p> Methods <p>A multi-degree-of-freedom dynamic model integrating multi-parameter excitation and coupling faults was established, validated with open-source experimental datasets. Multi-dimensional analysis methods including time domain, frequency domain, axis orbit, and phase diagram were used to extract fault features.</p> Results <p>Fault severity positively correlates with vibration intensity; the system exhibits complex chaotic motion under coupling faults, where bearing fault impulses tend to mask gear fault features. Outer raceway spalling causes stronger impacts than inner raceway spalling.</p> Conclusions <p>The established dynamic model effectively characterizes coupling fault behaviors, and the multi-dimensional analysis method enables reliable fault identification, laying a foundation for intelligent health monitoring systems of gear transmission systems.</p>