In　order　to　mitigate　the　double　near-far　effect,　we　focus　on　a　mobile　wireless-powered　communication　network　(WPCN),　where　sensor　nodes　harvest　energy　from　the　radio　frequency　(RF)　signal　of　the　mobile　energy　access　point　(EAP),　and　transmit　data　to　the　mobile　data　access　point　(DAP)　by　using　the　harvested　energy.　Only　the　sensor　nodes　with　energy　larger　than　a　threshold,　which　is　mainly　determined　by　the　energy　consumption　of　one　transmission,　have　opportunities　to　transmit　data.　Due　to　the　mobility　of　the　EAP　and　DAP,　the　distance　between　the　EAP　and　DAP　changes　over　time.　When　the　DAP　moves　into　the　operation　region　of　the　EAP,　the　EAP　and　DAP　could　not　work　simultaneously　due　to　the　severe　interference,　and　an　energy　harvesting　probability　is　employed　to　denote　the　probability　that　the　EAP　works　in　this　scenario.　The　purpose　of　this　paper　is　to　identify　the　optimal　transmission　policy,　i.e.,　the　optimal　pairing　of　the　energy　consumption　of　one　transmission　and　the　energy　harvesting　probability,　that　maximizes　the　throughput　of　the　WPCN　under　an　energy　causality　constraint.　By　analyzing　the　energy　causality　constraint,　we　show　that　the　WPCN　could　be　divided　into　an　energy-sufficient　state　and　an　energy-limited　state　by　the　pairing　of　the　energy　consumption　of　one　transmission　and　the　energy　harvesting　probability.　Since　the　energy　consumption　of　one　transmission　and　the　energy　harvesting　probability　are　jointly　intertwined　with　the　energy　causality　constraint,　making　the　joint　optimization　problem　intractable,　we　divide　the　throughput　maximization　problem　into　two　layers.　In　the　inner　problem,　we　investigate　the　optimal　energy　consumption　of　one　transmission　with　a　given　energy　harvesting　probability.　In　the　outer　problem,　we　derive　the　optimal　energy　harvesting　probability　based　on　the　obtained　optimal　energy　consumption　of　one　transmission.　According　to　the　aforementioned　investigations,　we　propose　a　two-layer　algorithm　to　obtain　the　specific　solution.　Numerical　results　are　conducted　to　validate　the　theoretical　results　and　the　efficiency　of　the　proposed　two-layer　algorithm.