Abstract: Due to the increase of open-pit exploration and shortage of land resources，the firms have to increase capacity in old dumps，that induced the security problem increasingly prominent.Taking a waste dump of Qidashan Iron Mine as a case，the feasibility for the capacity increase and heightening of the dump was analyzed.With the use of mechanical parameters obtained from the indoor experiments，slope model of waste dump was established based on the engineering geological investigation.The limit equilibrium method was adopted to calculate the slope safety factor of a dump without ground water or under low water，high water level in Qidashan Iron Mine，which is located on bedrock or clay layer，and obtain the influencing law of groundwater on mine slope safety.Especially when the dump is located in the clay layer，the slope safety factor falls rapidly as the underground water level raises，which seriously influences the slope safety.Through analyzing the slope stability at dump height of from 180 m to 230 m，it is shown that，within the range of from 180 m to 220 m，the dump safety coefficient is declined from 1.122 to 1.116，and at 230 m，the safety factor is increased to 1.142.The law of the slope stability under the changes of the water level and slope height provides a powerful basis for the slope safety evaluation and the determination of the regulation scheme.

Key words: Waste dump, Slope, Groundwater, Height, Stability analysis