The invention relates to a method for improving the complexity index of a deep shale gas fracture. The method is characterized in that when a fracturing design of the a deep shale gas well is performed, selection and an injection manner of a fracturing fluid, selection of a supporting agent, and the number of perforations are optimized and controlled, and an artificial main fracture can be opened and communicate with a natural fracture as much as possible in an extending process; extension of a single fracture is longer, expansion of the single fracture is wider, and finally the complexity of the deep shale gas fracture can be improved to the greatest extent. The method can be used for deep shale gas reservoirs having the depth of more than 3500 meters and in which the natural fractures containing carbonate minerals are distributed in a reconstruction range of the artificial main fracture, and a certain included angle is formed between the fracturing main fracture and the natural fractures. The method is reasonable in design, is simple in process, is easy to operate, is high in fracturing construction successful rate, can effectively increase the volume of deep shale gas segment fracturing fractures, can remarkably improve the fracturing construction effect, and can acquire more economic benefits.