Abstract: The monitoring of radio frequency signals has broad application prospects. This paper proposes a microwave photonic Radio Frequency (RF)signal monitoring system based on DSP. The system consists of the front-end microwave photonic signal receiving part and the back-end signal processing part. The RF signal is processed by optical down-conversion to get the Intermediate Frequency(IF) signal. After the Analog-to-Digital conversion, the FFT algorithm is 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 0.25 MHz, the dynamic range is 55 dB, sensitivity is -30 dBm. In addition, for further verification, the antenna is used to receive the mobile phone signal to realize the real-time monitoring of the mobile phone signal communication frequency band.