Abstract: In order to study the law of overburden rock movement and bed separation development in close distance coal seams，the movement of overburden rock when downward mining of close distance coal seams is simulated through similar material simulation experiment.The digital image correlation method is applied to measure displacement points and obtain displacement data of the measured points.The cluster analysis is used to classify the measured points and obtain the specific scope of the three zones under mining influence.According to the analysis on the displacement process of measured point，it has a feature of continuity and mutability.The expansion of the mining influence scope is in lateral spreading and vertical extension; When lower coal seam is explored，the maximal displacement point is behind the shortening distance of working face.Bed separation during upper coal seam mining is transformed into caving at lower coal seam mining.By analyzing the extension of the bed separation，it is concluded that the direction of the bed separation is in vertical and horizontal extension，and experiences the process of development-expansion-mutation-close.It is found that the bed separation rate curve of the row and column survey line is in double-humped shape.On row survey line，the causes for bed-separation rate curve，peak point size relations，and position change are analyzed，it is concluded that the peak point of the upper rock stratum are in internal displacement with that the lower rock stratum，the peak point nears to the fracture line，and the trough is located in the middle of goaf.From bed separation rate curve of the column survey line，it is obtained that the peak point is in bed separation.The closed area of bed separation is on the left of peak，and the development area is on the right.The trough on the right side of peak point is the position of key stratum; Peaks discontinuously moves and leaps to the right with coal seam mining.The discriminant method for weighting moment is given，finding that outer envelop curve exists on displacement curve of measuring point on mining influence zone.The identification method for key stratum is given，obtaining that the position of key stratum move up during lower coal seams mining.

Key words: Close-distance coal seams, Overburden rock movement, Cluster analysis, Digital image correlation, Bed separation, Key stratum