Abstract: Based on the significant impact of rainfall infiltration on coal waste dump slope stability, we established the calculation model of slope rainfall infiltration and writed calculation program, and calculated transient moisture content of slope after rain, the slope stability is analyzed through the limit equilibrium method and FLAC numerical simulation method before and after rain.The study shows that rainfall infiltration only affects moisture content of 3 meters depth below slope surface, slope is prone to occur surface shallow landslide; rainfall infiltration reduces the internal friction angle and cohesion of slope soil and slope safety factor; the maximum displacement and displacement distribution,the maximum shear strain and shear strain distribution and plastic zone increases significantly and slope safety reserve reduces significantly after rain.