Abstract: By means of analysis of the trailing flow field structure of different circle injectors,the relationship between the position of shock wave specific to injector diameter,and the pressure of inlet flow/pressure of environment was determined.From numerical simulation of circle injector with cylinder resonance tube and cone resonance tube,it is concluded that the necessary condition the intense resonance can occur within resonance tube lies in the position of resonance tube's entrance in the expand wave field;and if the position is in shock wave field,the resonance can not occur within resonance tube.Now the region where resonance occurs can be gained from free jet flow field by means of numerical simulation.The best matching between injector and resonance tube was obtained by analyzing the resonance heating performance variation with different diameter injectors.