Because　the　construction　of　dams　and　hydro-electric　power　stations　of　Liujiaxia　and　Yanguoxia　across　the　Yellow　River　in　West　Gansu　Province,　North-West　China,　inhabitants　in　the　reservoir　areas　were　resettled　in　Heifangtai　Loess　Platform.　Irrigation　thus　started　in　1968.　Perched　water　table　was　significantly　raised　and　resulted　in　many　loess　flow　failures　in　the　past　30　years.　This　type　of　landslide　was　often　featured　by　long　runout　distance,　high　speed　and　recurrence.　Laboratory　tests　along　ICU　and　CSD　stress　paths　were　performed.　It　is　shown　that　the　loess　has　a　strong　strain-softening　behavior　and　instability　can　occur　in　drained　condition　before　undrained　liquefaction.　The　failure　mechanism　of　loess　flow　can　be　interpreted　as　the　following　process:　with　increasing　perched　water　table,　collapse　in　loess　was　first　triggered　in　drained　condition　and　led　to　undrained　loading　to　adjacent　soil　in　the　lower　saturated　part　of　the　loess　platform.　Under　gravity　loading　applied　by　upper　dry　loess,　undrained　flow　failure　mobilized,　eventually.