Abstract: In this paper, based on lots of measured information, the Lyapunov exponent has been extracted from displacement and penetrating water quantity (seepage property)in the process of deformation failure for coal floor influenced by mining on pressure bearing water, and its chaos character has been studied. The analysis of actual examples indicates that the typical chaos character has been demonstrated in the process of deformation failture for coal floor. In addition, because the Lyapunov exponent of the seepage index for coal floor is larger than the displacement index,the seepage index is more sensitive than the displacement when it is used to describe the deformation failure character for coal floor.