Abstract: Th is paper is to study the selection of rat iona l slope rat io and slope deformat ionmechanism in loose de posits, w hich is the basis o f slope stability evaluat ion and supporting design. A m an- made slope comprising loose deposits in Southw estCh ina is taken as an example. B ased on study on the characteristics o f loose deposits, rationa l slope ratio is def ined according to the terrain. Tw o- dimensional fin ite e lementmethod is used to study deformation mechanism of the cut slope and to determ ine potent ial slide surface. A t las,t the suppo rt ing m easures are put for w ard according to the slope stability ana lysis. The slope has loose deposits of 70m in th ickness comprising a lluvia,l pro luv ia,l and debris f low deposits. The slope ratio is designed as 1: 0. 75 because the eng ineering flat is located at the low er part o f the slow slope, whose upper part is steeper. The resu lt of numerica l simu lation indicates that the cut slope area and the slope crest area generate tension stresses. The max imum shear stress concentrates at the low er part o f the slope, w h ich result in tension cracks at the slope top and shearing deformation at low er part o f the slope. W hen the shear ing deformation develops upw ards to the tension cracks, the slopew ou ld show an overa ll in stability. A ccording to the mechan ism analysis and result of slope stab ility evaluat ion, a synthetical supporting measure is pu t forw ard to con form the stab ility of the slope during ex cavation and operation periods. Them easure includes anchoring p ile, anchor cable fram e, anchor bo lt fram e, and dra inage.