Abstract: In order to study the influence of coal pillar in the upper coal seam on the stress transfer law of the floor rock, the “principal stress difference” is introduced innovatively as a dynamic index for the strata bearing state. It takes the place of the traditional methods of vertical stress, horizontal stress and shear stress, and gets rid of the research status that traditional models cannot quantitatively describe the degree of deformation and failure of coal and rock mass. In this paper, based on the traditional model research, the stress distribution state of the three stresses is obtained. Then the characteristic and solution formula of “principal stress difference” are further analyzed. Finally, the solution model shows that the transfer form of the principal stress difference on the floor is “fan-shaped diffusion”, and the stress curve in the shallow strata within 20 m of the floor is “double peak”. With the increase of buried depth, the curve gradually changes to a “single peak shape”, and the principal stress difference at the lower seam roof presents single peak, and the damage degree of the center line of the coal pillar floor is the largest.