This paper proposes a multi-frequency instantaneous signal detection scheme based on a non-uniform optical frequency comb. Furthermore, the paper takes the comb's power ratio with non-uniform power drop as a reference, utilizes the beat frequency power ratio of the signal to be measured and the comb to determine the frequency range of the signal, and then calculates the exact frequency of the signal based on the demodulated frequency information. Through the simulation, the instantaneous measurement of multi-frequency signals in the range of 0-20 GHz is realized, with an error ranging from 0 to 23 MHz. In addition, the paper analyzes the effects of factors on the measurement results, such as the laser's linewidth, the center frequency of fiber Bragg grating (FBG), the bias voltage of the electro-absorption modulator, and the phase difference of the optical hybrid coupler. Results show that the system is insensitive to changes in the laser's linewidth and the phase difference of the coupler, but the center frequency of FBG and the bias voltage of the modulator can affect the power ratio of the comb signal. When the power ratio is different to a large extent, the system is more stable, and the error gets smaller.