Abstract: When the stope is pseudo-inclined, the main roof of the goaf is basically non-rectangular. At this time, the fracture position and fracture rules of the goaf basic roof are different from that of the rectangular roof. To study the initial fracture characteristics of the basic roof of the pseudo-inclined stope, based on the mechanics theory of elastic thin plate. The initial failure mechanical model of right-angled trapezoidal basic roof plate structure was established, at the same time the bending formula of the right-angled trapezoidal thin plate was deduced, the fracture position and fracture rules were analyzed; at the same time According to the finite difference principle, the principal stress extreme value and position characteristics of the basic roof were analyzed, and the theoretical deduction results were verified. The results show that the internal force distribution of a right-angled trapezoidal thin plate with four sides fixed is roughly similar to that of a rectangular thin plate, but on four borders the position of the main bending moment extreme value is different from that of the rectangular thin plate. The latter are all located in the centre, while the formerly on the four sides of the thin plate moves to one side in the counterclockwise direction as a whole, and the Initial Breaking of the basic roof is inclined "O - X" type.