A　large　number　of　wheelchairs　are　manipulated　via　joysticks.　But　for　the　different　degree　of　the　handicapped,　joystick　does　not　fit　for　any　disabled　person　and　it　will　limit　the　users＇　hand　behaviour,　especially　in　sport　for　them.　This　paper　elaborates　a　more　effective　and　hands-free　method　to　control　the　intelligent　wheelchair　(IW),　and　describes　the　details　of　control　algorithm　on　the　omni-directional　platform.　The　algorithm　controls　the　IW＇s　directions　and　velocities　according　to　user＇s　different　sitting　postures.　Using　the　information　from　the　force　sensors　under　the　seat　surface,　the　different　2D　position　of　gravity　centre　will　be　calculated　out　to　control　the　intelligent　wheelchair　in　response　to　the　user＇s　leaning　in　different　directions　and　velocities.　Furthermore,　it　describes　the　motion　mathematical　model　of　the　omnidirectional　wheelchair　platform　and　provides　control　system　hardware　structure　as　well.　Experiment　results　eventually　indicate　that　the　sitting　postures　control　function　is　realized　accurately,　effectively　in　directions　and　velocities.