Abstract: The effects of unsteady separation,shock and viscosity on the stall flutter become now a main obstacle to aeroelastic study.The 2 D unsteady flow in an oscillating cascade is taken as composed of two parts:the steady mean flow and the small disturbance flow.The stall flutter is predicted by solving the steady Navier-Stokes equations and linearized Navier-Stokes equations separatedly,and can be simulated numerically for different kinds of flow separation,and then the unsteady separation can be treated effectively.The calculation results show that unsteady separation,shock and viscosity have significant effects on the stall flutter.Therefore,the unsteady pressure response in the separated zone cannot be taken as zero.