Abstract: For the safe and efficient production of hard roof working face, according to the characteristics of strata during the initial mining of hard roof, based on the theory of fracture mechanics, the mechanics model of forced roof caving of middle kerve was established. The expression of the initial weighting distance of the main roof was deduced and the influence law of rock fracture toughness and crack length on the initial weighting distance was also analyzed. The results show that the initial weighting distance of the main roof increases with the increase of the fracture toughness, decreases with the increase of the crack length and the main roof overburden. Under definite conditions of fracture toughness or the overburden load of the main roof, the initial weighting distance of the main roof remains unchanged when the artificial fracture length ratio reaches 0.6. The research results can provide the basis for the design and construction of similar projects.