Abstract: In the complex electromagnetic environment, the system for signal detection of radar reconnaissance receiver needs the abilities of wideband signal acquisition and processing, high probability of intercept and capture, and fast and accurate analysis. The digital radar reconnaissance system that applies the real-time spectrum analysis technology can highly enhance the capability of capturing and observing signals, and it is a new technology which has a very nice foreground in the application. First of all, the basic theory of real-time spectrum analysis technology and the two key techniques— frequency mask matching (FMM) and Digital phosphor technology (DPX) have been worked over. Then the method for signal detection based on cumulative spectrum which was made from DPX after FMM was put forward. Beside this, the performance in different conditions including single signal, double or multiple signals existing in the same receiver band was qualitatively analyzed. When there is more than one signal, the relationship of frequency position is divided into the separation, cross and containing, all the resolvent for every situation are particularly explained. Eventually the corresponding simulation tests were presented. There are three broadband signals in the frequency band, one signal not match the frequency mask and the other two signals do. Every 100 tests were done under the SNR of 5dB, 10dB, 15dB and 20dB. The analysis for the results and the conclusion was discussed followed. The simulating results has demonstrated that the multiple signals existing in the same time period can be analyzed effectively using the method proposed in this paper, which improves the performance of radar reconnaissance receiver.