Fractal theory is a very popular and active new theory and discipline in the world today. The concept of fractal was first put forward by American mathematician B B Mandelbort, who published an article entitled "How long is the British coastline?" in 1967. In the authoritative American magazine Science. A famous newspaper. As a curve, the coastline is characterized by extremely irregular and uneven, showing extremely tortuous and complicated changes. We can't distinguish this part of the coast from that part of the coast in shape and structure. This almost equal degree of irregularity and complexity shows that the coastline is self-similar, that is, the local shape is similar to the overall shape. Without buildings or other things as a reference, the coastline of 10 km photographed in the air will look very similar to the two enlarged coastline photos of 10 km. In fact, forms with self-similarity exist widely in nature, such as continuous mountains and rivers, floating clouds, cracks in rocks, trajectories of Brownian particles, tree crowns, cauliflower and cerebral cortex ... Mandelbrot called these forms similar to the whole to some extent fractal. 1975, he founded fractal geometry. On this basis, a science of studying fractal properties and its application is formed, which is called fractal theory.