In　order　to　investigate　the　influences　of　rainfall　on　deformation　characteristics　and　slope　instability　mechanism　of　the　residual　soil　slope,　a　real-time　monitoring　system,　artificial　rainfall　system　and　digital　photogrammetry　technology　were　used　to　conduct　a　geo-mechanical　modeling　test　under　the　different　location,　different　slope　angles,　different　density　and　different　rainfall　conditions.　Then　the　influence　of　rainfall　infiltration　on　body　displacement　and　matric　suction　was　observed.　Instability　risk　factor　should　be　considered　from　the　perspective　of　instability　mechanism　of　landslide　induced　by　rainfall.　The　variation　of　the　physical　quantity　of　slope　should　be　paid　much　attention.　Three　development　phases　of　slope　deformation　were　proposed　on　the　basis　of　slope　deformation　and　the　changing　law　of　matric　suction　with　time.　Meanwhile,　by　dint　of　instability　failure　processes　under　the　different　conditions,　the　rainfall-induced　residual　soil　slope　failure　mode　was　revealed.　The　results　show　that　matric　suction　and　body　deformation　of　slope　upper　part　change　greatly,　and　the　speed　is　fast.　However,　slope　lower　part　soil　change　slightly　with　low　speed.　Compared　with　the　gentle　slope　with　low　density,　the　anti-deformability　of　the　rainfall　infiltration　in　the　steep　slope　with　high　density　is　stronger.　As　the　energy　required　for　the　small　pore　structure　destruction　is　much　larger　than　that　of　the　large　pore　structure,　the　deformation　in　the　middle　part　of　the　gentle　slope　with　low　density　is　larger　than　that　of　the　upper　part　of　the　slope.　Considering　the　law　of　soil　suction,　time　variation　and　body　deformation,　three　stages　of　slope　deformation　development　are　put　forward,　namely,　the　initial　creep　stage,　accelerated　development　stage　and　sliding　failure　stage.　Meanwhile,　the　slope　instability　warning　factor　should　be　selected　from　the　instability　mechanism　of　rainfall-induced　landslides.　Besides,　the　matric　suction　of　slope　key　position　could　be　selected　as　the　slope　instability　warning　factor　for　unsupported　slope,　whilst　the　change　characteristics　of　matric　suction　and　supporting　structure　stresses　(deformation)　should　be　considered　together　as　the　instability　warning　factor　selection　for　supported　slope.　Based　on　the　failure　process　of　the　soil　slope　subjected　to　rainfall　infiltration,　the　failure　mode　is　observed.　It　starts　from　slope　surface　scouring,　and　gradually　develops　into　gully　erosion.　Subsequently,　the　local　failure　at　the　slope　toe　occurs,　and　the　damage　scope　extends　vertically　and　horizontally　and　finishes　with　a　global　shallow　landslide.　The　depth　of　slip　surface　is　1　to　3m,　and　this　kind　of　landslide　should　focus　on　the　slope　protection　to　reduce　possibility　of　slope　progressive　failure　as　much　as　possible.　The　results　provide　the　reference　for　constructing　a　prediction　model　of　landslides　induced　by　rainfall　in　the　southeast　coastal　areas.　©　2018,　Editorial　Department　of　China　Journal　of　Highway　and　Transport.　All　right　reserved.