Infiltration-runoff-slope　instability　mechanism　of　macropore　slope　under　heavy　rainfall　is　unclear.　This　paper　studied　its　instability　mechanism　with　an　improved　Green-Ampt　(GA)　model　considering　the　dual-porosity　(i.e.,　matrix　and　macropore)　and　ponding　condition,　and　proposed　the　infiltration　equations,　infiltration-runoff　coupled　model,　and　safety　factor　calculation　method.　Results　show　that　the　infiltration　processes　of　macropore　slope　can　be　divided　into　three　stages,　and　the　proposed　model　is　rational　by　a　comparative　analysis.　The　wetting　front　depth　of　the　traditional　unsaturated　slope　is　17.2%　larger　than　that　of　the　macropore　slope　in　the　early　rainfall　stage　and　27%　smaller　than　that　of　the　macropore　slope　in　the　late　rainfall　stage.　Then,　macropores　benefit　the　slope　stability　in　the　early　rainfall　but　not　in　the　latter.　Macropore　flow　does　not　occur　initially　but　becomes　pronounced　with　increasing　rainfall　duration.　The　equal　depth　of　the　wetting　front　in　the　two　domains　is　regarded　as　the　onset　criteria　of　macropore　flow.　Parameter　analysis　shows　that　macropore　flow　is　delayed　by　increasing　proportion　of　macropore　domain　(omega　f),　whereas　promoted　by　increasing　ratio　of　saturated　permeability　coefficients　between　the　two　domains　(mu).　The　increasing　trend　of　ponding　depth　is　sharp　at　first　and　then　grows　slowly.　Finally,　when　rainfall　duration　is　less　than　3　h,　omega　f　and　mu　have　no　significant　effect　on　the　safety　factor,　whereas　it　decreases　with　increasing　omega　f　and　increases　with　increasing　mu　under　longer　duration　(＞=　3　h).　With　the　increase　of　omega　f,　the　slope　maximum　instability　time　advances　by　10.5　h,　and　with　the　increase　of　mu,　the　slope　maximum　instability　time　delays　by　3.1　h.