Aiming at the problem that the distributed optical cable anti breakage monitoring system is susceptible to rainfall vibration,which causes system false alarm and interferes with the normal operation of the system,a set of distributed external damage monitoring system is built to collect signals in this paper.In order to distinguish rain signal and eliminate interference,the distinguishing characteristics of rainwater signal,artificial optical cable operation and mechanical construction signal in time domain and frequency domain are analyzed,and the feasibility of rainwater signal identification is studied.The results show that the intensity of the rain signal is high in the low frequency range and low in the high frequency range.The intensity of the rain signal decreases with the increase of frequency.Rainwater signal characteristics are quite different from artificial optical cable operation and mechanical construction in terms of influence range and frequency spectrum characteristics.Therefore,by identifying the rain signal,the false alarm rate of the external damage monitoring system can be reduced.