Abstract: The failure of the steam turbine last stage blades by abrupt increment of dynamic stress in some conditions has been analyzed, and it is confirmed that the main cause of this breakdown is self-excited vibration (flutter) of blades. The actuator disk method has been transplated from aeronautics to predict the steam turbine blade flutter. The actuator disk method only deals with the unsteadyflow field in front of and behind the cascade.The governing equation of the flow field is the linearized Ruler's Equation. To determine the constants of the equation solution, the cascade loss is correlated with the experimental data.The comparisons between the predictions and experimental results are acceptable.It is demonstrated that the abrupt increment of the blade dynamic stress at small volumetric flow is caused by large negative incidence stall flutter. It is discovered from the computations that at design conditions there may be a kind of high loaded unstall flutter which still hasn't been defined.