<p>Traditionally, during the nonlinear dynamic research of herringbone gear systems, it is common practice to consider the pressure angle and backlash as constants to simplify the modeling procedure. However, during practical operation, the deformation of bearings can cause the gears to move laterally, leading to changes in the parameters. To tackle this issue, this paper introduces an enhanced nonlinear dynamic model for herringbone gear systems that takes into account the time-varying characteristics of the pressure angle and backlash, along with the multi-state characteristics of gear meshing. Utilizing Lagrange’s Equations, the motion equations for the system are formulated and solved through numerical integration. Then, using rotational speed and initial backlash as variables, the differences in dynamic characteristics between the two models considering and not considering the time-varying pressure angle and backlash are compared. The findings reveal that incorporating the time-varying pressure angle and backlash significantly impacts the system’s motion period and influences the meshing state of gear. This research offers a theoretical foundation for future studies on herringbone gear systems.</p>