Abstract: Through field measurement and statistical analysis show that the support load of large mining height working face is generally larger and this is an increasing tendency with the increase of mining height,there is large and small periodic weighting in longwall face,and the static load of thick equivalent immediate roof is the basic load of support of longwall face. Through physical simulation experiments,the mechanism of immediate roof thickness increase and the move upward of hinge point of roof structure at large mining height longwall face are explored,the definition of “equiv- alent immediate roof” is proposed,and the“ double key strata” theory of large mining height longwall face in nearly shallow seam is established. Roof is mainly the “ double key strata” structure of large mining height longwall face in nearly shallow seam. According to the gob filling degree by equivalent immediate roof,the double key strata roof struc- ture can be divided into two types including“double voussoir beam” and “blique step voussior beam-voussoir beam”, and the common situation is" blique step voussior beam-voussoir beam" double key strata structure. The model of doub- le key strata roof structure is established,and the mechanism of large and small periodic weighting in longwall face is explored,and the calculation formula of the setting load of support and the support resistance is put forward,which pro- vide the theory basis for the roof control of large mining height longwall face in nearly shallow coal seam.