Abstract: Thermal power units to accept the power grid "Two Rules" assessment, there are often problems such as unstable combustion of boilers, violent fluctuation of main steam pressure, temperature and other operating parameters, and even excessive vibration. Based on the low-frequency vibration fault of steam turbine high and medium pressure rotor caused by steam flow disturbance, the mechanism of steam flow-induced vibration and bearing instability of steam turbine are studied, and the solution measures are proposed according to the vibration characteristics. The results show that the low-frequency vibration fault of high and medium pressure rotor can be eliminated by optimizing the flow characteristic function of steam turbine regulating valve and enhancing the stability of bearing bush.