Abstract: Considering the nonlinear oil-film force, a nonlinear dynamic model of rotor system was established, with Taylor transform method introduced to transform the original analysis model of rotor vibration system into a set of algebraic equations in discrete domain and analyze nonlinearly the dynamic characteristics of the 1st-span rotor vibration system. The responses of the rotor system were thus obtained with the bifurcation rule found out. The nonlinear phenomena of rotor system were represented by bifurcation diagram, frequency spectrum, Poincare mapping and trajectory of the journal center of the system. The results indicate that the motion state of rotor system will change in such a sequence as periodic-double periodic-periodic-quasi-periodic or change directly from periodic to chaos with the increase of rotate speed as the film force taken into account.