Abstract: Based on the hydrogeological conditions of Huoluowan coal mine, and combinated with the different rock mechanical parameters of overburden strata of coalbed 2^-2, this paper established a numerical model which simulated characteristics of overburden rock deformation and failure,and studied the development height of fissure zone and caving height of top wall at different stages of flighest mine pressure. Then according to the monitoring data of consumption of wash liquid at field experiment,the real growth height data were gotten. Contrasting the simulated results and the observed ones, the paper summarized the development height of hydraulic fractured zone between 33.6 and 37.8 m for working faces 22101, and the caving height was 9.6 m.Thus this was helpful to provide the scientific basis for evaluating the feasibility of mining under water and designing water prevention coal pillar for the study area.