The　experimental　results　of　boiling　and　condensation　co-existing　phase　change　heat　transfer　characteristics　in　a　small　and　vacuum　confined　space　under　low　heat　flux　conditions　are　presented.　The　working　medium　used　is　de-ionized　water,　the　heating　and　cooling　surfaces　are　polished　copper.　The　gap　of　the　confined　space　is　26　mm,　and　the　water　level　in　the　gap　is　set　at　10　mm,　12　mm,　14　mm　and　16　mm,　respectively.　Experimental　observation　and　results　show　that　boiling　and　condensation　processes　are　strongly　inter-related　and　have　significant　influences　over　each　other.　As　the　water　level　increases,　the　boiling　heat　transfer　coefficient　increases　at　first　and　then　decreases.　Analysis　of　the　standard　deviations　of　the　confined　space　pressure　shows　that　as　the　heat　flux　increases,　the　pressure　fluctuation　increases　first　and　then　tends　to　maintain　a　constant.　The　experimental　results　also　disclose　that　there　exists　an　optimum　water　filling　amount　at　which　both　the　boiling　and　the　condensation　heat　transfer　coefficient　acquire　their　maximum　value.