The　behaviors　of　the　sands　near　the　interface　between　saturated　loose　sand　and　a　sheet　pile　in　an　undrained　state　under　high　frequency　cyclic　shear　are　simulated　by　using　the　particle　flow　code　in　2-dimension　(PFC2D).　The　parameters　which　influence　the　volume　strain　and　porosity　of　loose　saturated　sand　near　the　interface　are　investigated.　Besides,　the　variation　of　pore　water　pressure　and　the　particle　motion　traces　near　the　interface　are　studied.　Numerical　simulation　results　show　that　shear-contraction　appears　in　saturated　loose　sand　during　high　frequency　cyclic　shear,　and　the　shear-contraction　is　obvious　when　the　values　of　the　parameters,　including　the　particle　friction　coefficient,　particle　stiffness,　shear　amplitude　and　shear　frequency,　are　smaller.　However,　it　is　also　obvious　when　the　values　of　the　parameters,　including　boundary　confining　pressure　and　frictional　coefficient,　are　larger.　The　porosity　of　the　sand　near　the　interface　decreases　firstly,　then　increases　a　little,　and　then　decreases　until　reaching　a　steady　value.　The　pore　water　pressure　near　the　interface　increases　cumulatively.　Sand　particles　near　the　interface　have　large　displacements,　and　the　value　of　the　displacement　become　larger　and　larger　with　the　reduction　of　the　distance　between　the　interface　and　sand　particles.