Abstract: Taking the geological conditions of the first coal face in a certain coal mine as the background, FLAC^3D software was used to study the effect of length and mining height of working face on the height of water-conducting fractured zone. The simulation results show that in the case of different mining height, the height of water-conducting fractured zone increases with the face length, when the face length is lower than 250 m, and the relationship between the height of water-conducting fractured zone and the face length is approximately linear; when the face length is between 250 m and 300 m, the height of water-conducting fractured zone increases rapidly, when the face length reaches to 300 m, the height of water-conducting fractured zone increases slowly, the maximum height of water-conducting fractured zone appeared, when the face length is 350 m; the relationship between the height of water-conducting fractured zone and the mining height is approximately linear.