The invention discloses an ADAMS-based nonlinear dynamics modeling method for a planetary gear train. According to the modeling method, time-variant meshing stiffness, time-variant meshing damping and related parametric excitation are introduced in a model; the built model is high in universality and can perform dynamics simulation of the planetary gear train in any working condition; and a calculation result of gear meshing force is more accurate, the influence of the accuracy of the geometric shape of the built model on the accuracy of the calculation result is effectively avoided, the calculation speed is high, and the precision is high. In addition, an established gear meshing force equation provided by the method is suitable for planetary gear trains with different structures, such as a planetary gear train with a fixed gear ring and a differential planetary gear train.