Abstract: Steam flow exciting force of the first eight stages under different loads was obtained through numerical simulation, which was equivalent to gas bearing applied to the rotor to explore the influence of steam flow excited vibration on vibration characteristics of a steam turbine rotor. The high pressure cylinder rotor of a 1000MW ultra-supercritical steam turbine was modeled by the lumped parameter method, and the anisotropic support model was established. The influence of steam flow excited vibration on rotor vibration characteristics was obtained by using Riccati transfer matrix method. The results show that when the load is greater, the azimuth angle of ellipse trajectory is greater. With the increasing of load, the first-order natural speed increases and the second-order decreases. Steam flow exciting force has little effect on the natural speed. As the load increases, the first and second-order logarithmic decrement rates decrease. When the rated load is reached, the logarithmic decrement rate is 0.012, which is 97.5% lower than that without steam flow exciting force, and the rotor stability margin is seriously insufficient, and it is easy to lose stability.