Abstract: Considering that the power level drops significantly and steam flow separates from the outlet of rotor blades in the last stage of steam turbine at low load conditions,the last stage in whole working conditions was calculated and the height of flow separation in different volume flow was obtained.Different conditions of turbine under the same flow path with nozzle governing and throttle governing were calculated respectively.The results show that the flow separation bubble and separation height increased dramatically when volume flow decreased;the throttle governing at low load conditions increased the steam rate of turbine and the enthalpy drop of pressure stage,while reduced the changes of power distribution under the influence of steam parameters changing;in the same load,the throttle governing increased the volume flow in last stage,and reduced the separation height of rotor blades accordingly;it was propitious to improve the flow of the last stage at low load conditions,and postpone the emergence of zero power conditions.