Effect of water flow or seepage is very important factor in determining the stability of the slope, especially on the clay.In this paper, the soil analyzed in the Polytechnic of Padang, and soil samples taken at the edge of the slope.Soil samples taken were disturb sample. Laboratory test carried out by the addition of water content variation into the soil samples , the addition of water content starting from the below and above the Liquid Limit. The addition of water content in soil samples starting from 40%, 45%, 50%, 55% and 60%, in each variation do the test of shear strength and slope stability analysis with Geoslope sofware.The analysis result obtained the value of Liquid limit is 66 % and the classification of the soil is MH-OH (clay-silt). If the moisture content of the soil above 40 %, the value of shear strength drops drastically followed by the decline value of the safety factor of the slope. The decline value of the safety factor of the slope reaches 77 %.