Aiming at surge problem of a certain engine,this paper tries to find out the starting stage resulting in rotating stall/surge in an experimental way.A data processing program based on Matlab language is developed.A criterion based on stall theories is proposed to identify the first stall stage of the compressor.During data processing,spectrum theories and time domain methods are employed.The results of experiment show that the engine stalls first at the 3rd compressor stage,and stalls simultaneously at different height of blades.The followed experiments proved the verity of the judgement.