Fiber laser doppler velocimetry has the advantages of high measurement accuracy, wide measurement range and non-contact measurement. Usually, fiber optic bundles are used in traditional measurement systems. Multi-core fiber (MCF) is a new structure of optical fiber with multiple cores in the same cladding and a uniform core layout. Compared to traditional fiber bundles, multi-core fibers have advantages in integration and volume. Therefore, by taking advantage of the special spatial arrangement of cores and compact structure of MCF, we investigate the laser doppler velocimetry system. The main work includes:1. Simulation and analysis of double-beam interference fringes based on MCF; 2. Construct a laser doppler velocimetry system based on MCF, and verify the feasibility of the experimental system. Our method provides an effective solution for fiber laser doppler velocimetry.