To　guarantee　collision-free　locomotion　of　avatar　in　collaborative　virtual　environment,　a　collision　detection　scheme　should　be　provided　to　prevent　avatar　from　not　only　penetrating　into　all　other　virtual　obstacles　but　also　colliding　with　all　other　avatars　without　stalling　any　avatar　with　ultimate　goal　of　user＇s　senses　of　presence,　reality　and　immersion.　This　paper　discussed　how　to　design　a　horizontal　collision　detection　scheme　for　avatar　with　avatar.　First,　it　proposed　several　design　considerations　for　a　horizontal　collision　detection　scheme.　Second,　through　collision　precaution　and　collision　repulsive　field　that　are　two　attached　properties　to　avatars,　the　process　procedure　of　the　whole　collision　detection　is　divided　into　three　processes:　collision　determination,　collision　avoidance　and　path　amendment.　On　the　basis　of　above　works,　this　paper　presented　a　new　horizontal　collision　detection　scheme　AACD　for　avatar　with　avatar　in　collaborative　virtual　environment.　Finally,　architecture　of　AACD　is　described　in　details　in　this　paper.　©　2005　IEEE.