An　experimental　study　was　carried　out　to　investigate　the　thermal　characteristics　of　an　eccentric　annular　wickless　heat　pipe　(EAWHP)　with　deionized　water　as　a　working　fluid.　The　eccentric　annular　wickless　heat　pipe　was　sealed　by　a　high　vacuum　valve　which　is　capable　of　changing　the　filling　ratio.　The　experiments　were　performed　in　the　range　of　343.15-373.15　K　operating　temperature　and　15-60%　filling　ratio　under　natural　convection　and　forced　convection.　The　temperature　stability,　uniformity,　and　distribution　of　the　evaporator　wall　outer　surface　and　the　condenser　wall　inner　surface　of　the　eccentric　annular　wickless　heat　pipe　are　affected　by　various　factors,　such　as　the　filling　ratio,　the　mounting　location　of　the　heater　controller　sensor,　and　the　cooling　ability　of　the　condenser　section.　The　results　show　that　the　larger　filling　ratio,　lower　operating　temperature,　and　the　upper　temperature　control　point　have　been　found　to　be　very　helpful　for　optimizing　the　temperature　stability　and　uniformity　in　the　condenser　wall　inner　surface　under　our　experimental　conditions.　The　temperature　stability　of　the　central　of　condenser　wall　inner　surface　can　reach　0.048　K　for　2　h,　while　the　accuracy　of　the　device　for　controlling　temperature　lies　within　+/-　2.0　K.　The　condenser　wall　inner　surface　temperature　uniformity　can　be　reached　at　0.142　K,　while　that　of　the　evaporator　wall　outer　surface　is　2.676　K.　Analysis　of　the　evaporator　wall　outer　surface　temperature　distributions　using　a　method　of　thermal　resistance　network　is　also　presented.　The　ability　to　maintain　constant　evaporator　temperature　makes　the　eccentric　annular　wickless　heat　pipes　effective　devices　for　use　in　temperature　calibration　field.