The monitoring of radio frequency signals has broad application prospects. A microwave photon Radio Frequency (RF) signal monitoring system based on DSP is proposed. The system consisted of the front-end microwave photonic signal receiving part and the back-end signal processing part. The RF signal was processed by optical down-conversion to get the Intermediate Frequency (IF) signal. After the Analog-to-Digital conversion, the FFT algorithm was applied on DSP to complete the spectrum analysis of the received signal. The experimental results show that the system can complete the RF signal monitoring. The frequency measurement error is less than 0.25MHz, the dynamic range is 55dB, and the sensitivity is -30dBm. In addition, for further verification, the antenna was used to receive the mobile phone signal to realize the real-time monitoring of the mobile phone signal communication frequency band.