Abstract: The rock mass quality and the water blocking performance in the floor was evaluated, with extraction of seam No.9 in Xingtai coal mine as an example. First of all, analysis of geological structures of coal seam floor was conducted, and the rock mechanics parameters were obtained; the ground stress was tested, the nature of ground stress was grasped in this region; The rock pressure behavior was studied, the step of the initial collapse and step of the pressure cycle of working face were obtained. The depth of floor damage in fully mechanized and coal top-coal mining face was tested. On the basis of the above-mentioned study, by using three-dimensional non-linear solid-liquid coupling calculation of rock hydraulics, and by means of non-linear numerical simulation software ANSYS, three-dimensional numerical simulation model was established. The stress distribution of coal seam floor of different stages of mining was studied according to the mine hydrogeological, engineering geological characteristics and conditions of mining technology. Numerical simulation results show that the possibility of inrush water was as condition Ⅳ > condition Ⅲ> condition > condition,th Ⅱ Ⅰ e basis for selecting the first coal mining of 9th coal seam was provided