Mechanism　of　activated　carbon　desulfurization　under　the　condition　of　desorption　by　water　is　investigated　according　to　the　results　of　adsorbing　performance　experiments　with　different　adsorbents.　Analysis　and　estimation　of　reaction　space　in　the　whole　reaction　process　are　offered　on　the　basis　of　Zawadzki＇s　desulfurization　theory.　It　is　indicated　that　the　effective　adsorption　sites　germinate　only　in　a　certain　reaction　space　where　the　appropriate　distances　and　configurations　among　reactant　molecules　have　been　formed.　Therefore,　the　distribution　of　aperture　of　adsorbent　is　a　crucial　factor　in　the　adsorption　process.　The　best　utilization　is　gained　when　the　aperture　width　approaches　to　1　nm.　And　a　type　of　adsorbent　MHY30,　whose　aperture　amplitude　is　over　1　nm　and　granule　size　about　3　mm,　is　suggested　to　be　adopted.