Abstract: The dynamic model of the angular wobbly of the gas film and seal rings was established,and the gas film angular rigidity,critical moment of inertia and the angular wobbly two-dimensional vibration equations was solved by using the perturbation method and the Runge-Kutta method,then the seal structure instability parameters were obtained,quantitative relation of critical moment of inertia and the angle and the nonlinear dynamic behavior of the vibration was analyzed.The simulation results was verified by testing.The results show that there are instability point-fields in the spiral angle range(usually 60°-80°) of the static optimization,and 16 points in the special case are found and the amplitude will be changed but the spiral angle on the instability point-fields will not be changed under the variable conditions(medium pressure and speed is changed),and the results coincide well with experimental results.