As the representative of the third generation semiconductor materials, SiC has excellent physical and chemical properties. With the development of materials and applications, SiC substrates are increasingly important in aerospace power supply, electric vehicles, smart power grids, rail transit, industrial motors and other fields. Compared with the first generation of semiconductor materials such as Si and the second generation of semiconductor materials such as GaAs, the quality of SiC substrate which has a lot of room for improvement, is the current research and development and industry hot spot. The detection and reduction of SiC single crystal defects, especially one-dimensional dislocation defects, is an important research content in the last ten years. This review focuses on the formation of dislocation in SiC, dislocation detection techniques, methods of reducing dislocation density and the optimization level of dislocation in SiC single crystal in recent years. Finally, the paper puts forward the direction of SiC's further breakthrough and development.