In the 1970s, researchers developed the concept of the free electron laser and built the far infrared free electron laser. Subsequently, many countries have carried out relevant theoretical research and experimental exploration, and in the early 21st century, the X-ray band of the free electron laser was built. X-ray free electron laser is a large scientific research device based on linear electron accelerator, which can produce ultra-short and ultra-coherent X-ray laser pulses with adjustable wavelength. In the past ten years, X-ray free electron laser has attracted wide attention from the scientific community. Thanks to the strong investment and support from various countries, it has achieved rapid development in a very short period of time and played an important role in the fields of physics, chemistry, life science and materials science. In this paper, the basic principle, development and application of X-ray free electron laser are briefly introduced.