The fluid loss of fracturing fluid in coal rock is closely related to joints and micro-fractures in coal. Based on the analysis of the classical fluid loss model, the relationship between fracturing fluid loss and coal reservoir pore fracture and permeability was studied. During the fracturing process, the fracturing fluid extended to the fracture wall facing the coal reservoir. The main channels of percolation were the tiny fractures in the coal reservoir and the pores on the main fracture wall. Porosity of coal reservoir was one of the decisive factors affecting the fluid loss of fracturing fluid. Matrix permeability and fracture permeability jointly affected the fluid loss rate of fracturing fluid. During the fracturing implementation, the fluid loss of the fracturing fluid was not harmful, and only through partial filtration of the fracturing fluid, the filtrate could enter some small micro-cracks near the main crack, and the micro-cracks were mutually the connections, even to the main cracks, eventually formed a complex network of cracks, which was the mechanism for the effective fracturing transformation of the fluid loss.