Abstract: A finite element model was established for ground standing type bearing support of LP rotor for a 1 000 MW nuclear power half-speed turbine-generator set with spring foundation, with which the support stiffness was analyzed using 3D finite element software Ansys. Effects of the support stiffness on critical speed of the LP rotor were calculated and analyzed on the basis of above stiffness analysis. Results show that the value of bearing support stiffness calculated with the model is different from but in same order of maganitude with that of empirical value. The critical speed of LP rotor is greatly affected by the bearing support stiffness lower than a certain value, therefore for safety operation purposes, the bearing supports should be designed with higher stiffness.