Abstract: An iterative precise integration method is proposed to calculate the transient response of rotor-bearing systems.The state transfer matrices are calculated with the precise integration method and the precise solutions of homogeneous equations can be obtained.Therefore an implicit integration procedure is given in the light of the characteristics of oil film forces.The matrices and vectors are partitioned and the dimension of the nonlinear equations is reduced greatly.The integration method presented is unconditionally stable and can assure high precision and efficiency.