Abstract: In order to get the development law of water-flowing fractured zone of thin bedrock in Sima Mine,we analyzed the distribution characteristics and rock mechanics characteristics of the thin bedrock.Then the empirical formula was used to calculate the development height of water-flowing fractured zone.At the same time, the coal mining was simulated by using the RFPA^2D.The results show that the general trend of thin bedrock of 3^# coal seam is synclinal.The local of the thin bedrock has small uplift and grooves.The range of the thickness of the thin bedrock is 30 m to 80 m. The strength of the whole based rock pillar is over 40 MPa.So it belongs to hard rock. The empirical formula was used,and the height of the water flowing fractured zone of 3^# coal seam in Sima mine is from 47.3 m to 83.5 m. The result is basically consistent with the numerical simulation. Numerical simulation obtained the maximum development height of 85 m.