Abstract: Blade is the key component of wind turbine, and its performance will affect the whole system. The working environment of a wind turbine is complex, and the blades are easy to be damaged. The expansion of surface damage such as cracks can not be found in time, which may lead to irreversible damage to the structure and even damage to the tower. Therefore, blade damage detection is of great significance to the safe and efficient operation of a wind turbine, and reduction of the operation and maintenance cost. This paper comprehensively introduces the causes and types of wind turbine blade damage, comprehensively analyses and summarizes the existing blade detection technology, discusses the advantages, disadvantages and research hotspots of the existing methods, and introduces the robot composite detection technology equipped with multiple sensors and the commonly used data analysis algorithm in the detection technology. At the same time, the application of various damage detection methods of wind turbine blades is also given. Finally, the future development trend of wind turbine blade damage detection technology is introduced.