In recent years， the recognition of non-cooperative communication signals has become research focus in the field of communication countermeasures. In this paper， a recognition method of non-cooperative communication signals based on modulation is proposed. The characteristic parameters of non-cooperative communication signals are extracted by signal processing algorithm， and then the signal modulation mode is identified based on the decision tree combined with discriminant process. Various analog and digital modulation signals can be identified by this method. For frequency shift keying（FSK） signal， this paper proposes to construct a new signal by extracting the phase difference between the sampling points of the baseband signal， and the modulation type of the original signal is determined according to the recognition result of the constructed signal， avoiding the need for prior information. The signal modulation recognition method proposed in this paper has low computational cost and good real-time performance. Matlab simulation results show that this method has good recognition rate， and the correctness and feasibility of this method are proved.