A　call　admission　control　(CAC)　scheme　used　in　hierarchical　mobile　IPv6　(HMIPv6)　network　is　proposed,　which　solves　the　ideal　call　number　of　each　cell　adaptively　to　maximize　system＇s　profits,　under　the　restriction　of　system＇s　overload　probability　and　capacity　and　in　terms　of　hosts＇　mobility　characteristics　and　call　characteristics.　The　CAC　threshold　of　each　cell　used　in　making　decisions　of　accepting　or　rejecting　a　new　call　by　network　is　solved　by　establishing　a　Markov　model　in　HMIPv6　network,　which　can　make　system＇s　call　number　up　to　the　ideal　value.　Simulation　analyzes　the　factors　affecting　the　optimal　regional　size,　providing　a　reference　for　designing　a　dynamic　regional　mobility　management　scheme.　The　simulation　analyses　reveal　that　with　the　increase　of　calls＇　handoff　probability　and　average　duration　time,　the　optimal　regional　size　increases　while　the　regional　ideal　call　number　decreases;　and　with　the　restriction　of　overload　probability　relaxes,　the　new　call　blocking　probability　(CBP)　comes　down　while　the　handoff　dropping　probability　(HDP)　goes　up.　Finally,　a　performance　comparison　result　between　the　proposed　scheme　and　the　mobile　IP　reservation　(MIR)　scheme　demonstrates　that　the　average　values　of　CBP　and　HDP　in　the　proposed　scheme　are　lower　than　those　in　MIR　during　2000　simulation　intervals,　which　means　the　optimization　is　realized.