Abstract: It is certainly desirable to know steady inlet/engine matching state at any point of flight envelope either for development or for flight test of a new plane. But this task is complexed because of the uncertainty of inlet characteristics itself, i.e, it is not only a function of inlet geometry, but of flight Mach number, angle of attack, slip angle and of the fact that inlet wind tunne test can only be performed at limited combinations of the variables above. A method for rapid estimation of inlet/engine steady matching state and stability margin is presented in this paper, which is based on the concepts of subcriti-cal level （or Buzz margin and supercritical level or "ithing" oscilation margin） and generalized inlet characteristics, Practice has shown its availability.