To adapt modern electronic reconnaissance techniques to the electromagnetic environment of dense signal, broadband spectrum, and large dynamic range, a coherent optical signal processing method based on acousto-optic deflector is presented. The relationship between the changes of radio-frequency signal frequency and Bragg diffraction angle is analyzed, spatial filtering characteristic resulted from acousto-optic deflection effects is discussed. On the basis of theoretical analysis, the experimental system using acousto-optic technique is established to achieve coherent optical signal detection in the visible light range. The feasibility of this method is proved by computer simulation results. Experimental results show that if the system uses a single-frequency laser with wavelength of 630 nm and a acousto-optic deflector with bandwidth of 200 MHz, the frequency resolution is better than 1 MHz, the space separation effect of frequency signal is obvious, and the received sensitivity and signal-to-noise ratio (SNR) are improved.