Abstract: In order to obtain tiny deformation law in thickness alluvium, this paper analyzed the deformation in thickness alluvium under the condition of mining in N 0.7267 coal mining face of Yaoqiao Coal Mine, and analyzed the mechanism for the engineering phenomenon. The results showed that the deformation in thickness all uvium had random varying characteristic and topped out at 3. 65 mm in the horizontal direction; the deformation in thickness alluvium was in a compressed state as a W hole and topped out at 18. 67 mm in the vertical direction, the bottom aquifer hydrophobic compression and aquiclude water- swelling, less affected on the ground depr ession. The stress redistribution and random medium rearrangement caused horizontal movement of layers. The compression of aquifer was mainly caused by hydroph obicity in strata, which made the effective stress increased, and the expansion of aquiclude was mainly caused by hydrating swelling of clay layers.