The rotor's dynamic performances largely depend on bearing's parameters.On the base of former eight-parameter model,an improved model is advanced which calculates the ununiformity force due to the tiny obliquity of rotor axis.By simplification to the center of bearing,a force and a moment are educed.An example is given to compare the results of two models by calculating the rotors critical speed through the FEM(Finite Element Method).The results indicate that an obvious error will be brought about if the rigidity of bearing were much larger.Therefore,it is necessarily to introduce the improved model to the rotor's dynamic design,which has a significant meaning to increase the precision of calculation in rotor's system design.