Abstract: Based on saturated-unsaturated seepage finite element theory，the infiltration mechanism and characteristics of coarse grain of dumping under the condition of rainfall analysis in a mining area in Shanxi were investigated.On basis on the sieving test of slags in different dumping period，the unsaturated permeability coefficient was derived through particle size distribution curve.Combined with an engineering example，and with use of the numerical simulation software Geostudio，the finite element model of slope seepage was established，and quantitative analysis on the effect of rainfall stage on for coarse mine stability was made.Results showed that the particularity size and structure of the coarse grain mine results that the change trend of matric suction along with saturation is not significant.While，the previous dump has a better compactness，and the rainfall seepage mainly comes to the third period of dumping with a greater hydraulic conductivity.At the same time，the unobstructed seepage channel in dump can easily cause a local rapid rise in hydraulic gradient，and also because of its fast drainage process，the stability coefficient of coarse mine has a not obvious lagging.But in a short time after the rain，it will have a certain amount of rebound.

Key words: Dumping site, Rainfall infiltration, Unsaturated theory, Slope stability