Abstract: Slope stability is an important factor to ensure the safety and efficiency of open-pit coal mine.In order to study the influence of water drainage on the seepage field and the stability of non working slope in Shengli open pit mine. This paper takes the non working side slope of Shengli open-pit coal mine as the research object,the formation reason of the water resistance mechanism of the inner drainage field is analyzed by using the change rule of the porosity and permeability coefficient of the waste;based on the knowledge of soil mechanics, the equivalent substitution of permeability coefficient in the direction of vertical and parallel bedding for the slope of Inner Dump;the seepage path and water level distribution in the rock mass of the slope before the inner drainage are simulated;the SEEP/W module of Geo-Studio software is used to build the model, and the seepage field changes caused by different dumping height and width under the same boundary conditions are studied.The variation of pore water pressure was analyzed and the slope stability was evaluated with SLOPE/W module.The results show that the main reason for the change of seepage field in the non-working side is the formation of the water resistance of the waste in the inner dump.Under the influence of internal dumping blocking water,the variation range of excessive pore water pressure in the slope increases,and the pore water pressure of the shallow soil is basically maintained at about -10 kPa, the soil is nearly saturated, and the local pore water pressure is 0,showing the stagnant water in the upper layer and water seepage at the top of the slope.With the gradual shift of the slide towards the inner drainage site,the safety coefficient of the slope increased from the initial state to 1.834 and then gradually dropped to 1.673,and the overall stability was improved compared with that before the inner drainage.