Abstract: In order to improve the performance of the laser Doppler velocimetry system and enhance the adaptability of the system to application scenarios, the characteristics of the two main frequency shift devices of electro-optic and acousto-optic were compared. Starting from the principle of frequency shifting of devices, a simplified method of analyzing frequency transformation relations was proposed. The frequency shift characteristics of the two devices in the laser Doppler velocimetry system was theoretically studied, all-fiber laser velocimetry system link of a lithium niobate electro-optic modulation and acousto-optic frequency shift were bulit. The test frequency characteristics and the theoretical characteristics was compared. A new type of acousto-electric hybrid modulation laser Doppler velocity measurement system was proposed. The results show that the new system has the advantages that the acousto-optic frequency shift speed measurement system can measure the movement direction and speed of the moving target, and accomplish the multi-frequency correction of electro-optic modulation speed measurement system, the relative error of frequency measurement is small, and the dynamic range is large. By studying the frequency characteristics of the two frequency shifting methods, it provides theoretical and experimental support for the design of high-performance laser Doppler velocity measurement systems.