Abstract: in order to achieve the formation mechanism of the arch shell large structure of overburden in the coal mining face with the multi layer hard roof.taking the ultra thick seam mining with Carboniferous multi ayer hard roof inTongxin Mine of Datong Mlining Area as an engineeringbackground,based on the key stratum theory,the paper had an analysis on the breakdown features of the muti layer hard roof in the ful-mechanized ultra thick seam mining face in No. 3-5 seam of Tongxin Mine and the overburden strueture features of the large space mining fac. An elastc plate theory was applied to establish an arch shell balanced large structure mechanics model and the mathematical model of the hard overburden above the large space mining face. the study showed that the arch shell balanced large structure theored to well reveal the large and small periodic roof weighting,.large mining infuence scope,easy occurred strong mine rock pressure and other special mine rock pressure phenomenon mechanism occurred in the mining process of No.8105,No.8106 and other coal mining face in Tongin Mine. The study results could provide the theoretical basis to the mine rock pressure control of the coal mining face in the ulra thick seam with Carboniferous hard roof in Datong Mining Area.