Numerical investigations on the effect of inlet preswirl on the unsteady flow field and fluid excitation rotordynamics characteristics of labyrinth seal at high pressure environments was presented by solving the unsteady ReynoldsAveraged NavierStokes (RANS) equation based on the multifrequency elliptical orbit rotor whirling mode and dynamic mesh technique.Comparison of the swirl ratio,circumferential pressure in labyrinth seal cavity and rotordynamic coefficients of labyrinth seal among three inlet preswirl ratio 02,05 and 07 was conducted.The obtained results show that the labyrinth seal under high pressure environment possesses positive and frequencyindependent direct stiffness coefficients.With an increase of inlet preswirl,the effective damping of the labyrinth seal is decreased and the crossover frequency of the effectiveness damping is increased significantly.The crossover frequency of the effective damping coefficient is increased from 391 Hz to 554 Hz when the preswirl ratio is increased from 05 to 07.The increase of the inlet preswirl results in the increase of the circumferential swirl ratio in the labyrinth seal cavity as well as the nonuniformity pressure distribution along the circumferential direction,which will lead to the increase of the direct stiffness coefficients and crosscoupling stiffness Kxy coefficients.In addition,the direct damping and effective damping coefficients of labyrinth seal at high frequencies(f>30 Hz) are obviously decreased with the increase of the inlet preswirl.