In order to monitor the radiation noise of submarine in the real time is come true, on the basis of basic characteristics and uses of monitoring submarine noise on-board equipments which are often used in worldwide navy were introduced, method of extracting characteristic frequency spectrum of main noise sources for submarine was studied by use of acceleration sensors, and then displaying and setting threshold of self-noise hydrophone was studied based on the condition monitoring, and setting threshold of self-noise hydrophone was studied based on far-field measurement. The results demonstrate that the characteristic spectrums of main noise sources from submarine can be picked up and threshold of self-noise hydrophone can be set by use the method of this paper, which can provide the base for monitoring the radiation noise of submarine in the real time.