With the development of modern communication technology, traditional electronic instantaneous frequency measurement systems face bottlenecks such as bandwidth and speed, and can no longer meet the needs of modern electronic warfare. This paper proposes a scheme of multiple microwave signal instantaneous frequency measurement. The light source is provided by a single laser and divided into two branches by a splitter. The upper branch microwave signal is modulated onto the optical carrier by a Mach-Zehnder modulator, then used as the pump light, and the lower branch is used to generate an optical frequency comb with high flatness and the same interval. The pump is split into multiple channels by a demultiplexer, and each frequency comb of the Optical Frequency Comb(OFC) is sent into the corresponding channel through the optical circulator. In each channel, the pumb and the frequency comb are sent into dispersion-shifted fiber simultaneously. The Brillouin scattering can be stimulated if the frequency of the pumb is a Brillouin frequency shift higher than the frequency of the comb, and brillouin gain occurs in this channel. Thus frequency-space mapping is achieved. The frequency of the microwave signal can be judged by monitoring the change in the intensity of the output optical signal of the corresponding channel. In the simulation experiment, the instantaneous frequency measurement of the single-frequency signal and the multi-frequency signal in the range of 0~25 GHz is carried out. The simulation results show that the output power of the channel with the microwave signal to be measured is significantly increased compared with other channels. The method can measure single-frequency or multi-frequency microwave signals from 0.1 GHz to 25 GHz with a resolution of 0.1 GHz and a measurement error of ±0.05 GHz. In addition, the influence of the offset point drift of the Mach-Zindel modulator on accuracy of the measurement is analyzed. The simulation results show that the scheme can suppress the influence of the offset point drift on the measurement results to a certain extent, which proves the feasibility and reliability of the scheme. Using the photon assisted method, the microwave frequency can be measured in large frequency range in real time, which has a wide measurement range and strong anti-electromagnetic interference ability, and has a broad application prospect in electronic warfare system.