Dynamic analysis can provide a theoretical basis for controlling vibration and noise in gear systems, as well as calculating strength under dynamic conditions. This paper takes 6HP26 automatic transmission as the research object, takes the fifth-gear transmission as an example, adopts the centralized mass method to establish its translation-torsion coupling dynamic model, and analyzes the displacement response, torsional linear acceleration time-domain response and spectrogram of each component. This provides a reference for reducing vibration and noise in the system.