We　report　by　molecular　dynamics　(MD)　that　the　armchair　single-walled　carbon　nanotubes　(ACNTs)　has　a　multistability　rather　than　bistability　as　the　diameters　are　above　a　threshold　value　of　about　3.5　nm.　The　present　work　demonstrates　that　ACNTs　have　four　stable　states　when　the　diameters　are　above　the　threshold　value.　The　newly　found　stable　states　are　caused　by　surface　van　der　Waals　forces.　We　also　find　the　transformation　between　different　stable　states　can　be　realized　by　external　loading　or　temperature.　These　imply　the　ACNTs　have　a　great　potential　application　in　the　future　nanoscale　devices.