The flush airdata sensing system is much better than the traditional airdata system,and it depends on the pressure sensors allocated on the forebody of aircraft to derive the airdata indirectly.In this paper,at first the pressure model is showed briefly.And then an analysis is given,which is about the effect of the internal sensors geometry appearence on system performance;and the aerodynamic model of the pressure sensors has been developed,furthermore,the design criteria for the pressure sensors of FADS system has been formulated.Finally,the result of the simulation has been showed.