Abstract: A model to relate the mechanical behaviour of roof strata overlying horizontal/gently inclined orebody is built with hard roof as elastic plate and based on the theory of plates and shells to obtain the maximum stress of roof deflection，bending moment and board. Combining with field observations，it is considered that the roof deflection can measure the supporting force. In the forming process of the roof deflection，the maximum loading may be generated at the regional support with largest deflection. When the stress generated is equal to or greater than the ultimate strength of the supporting body，this supporting body will be destroyed. Subsequently，this part of stress is gradually transferred into the surrounding supporting body. Combined with field observation and roof instability analysis，it is indicated that the closer to the roof，the faster the support damaged at maximum deflection region，or the worst.Therefore，according to the roof deflection that may appear，it is rational to arrange the pillar or make filling to realize the efficient control of the ground pressure and the optimal technique and economy.

Key words: Theory of plates and shells, Deflection, Roof stability, Ground pressure