Single　mode　lasers,　particularly　red-green-blue　(RGB)　colors,　have　attracted　wide　attention　due　to　their　potential　applications　in　the　photonic　field.　Here,　we　realize　the　RGB　single　mode　lasing　in　a　hybrid　two-dimension　and　three-dimension　(2D-3D)　hybrid　microcavity　(mu-cavity)　with　a　low　threshold.　The　hybrid　2D-3D　mu-cavity　consists　of　a　polymer　fiber　and　a　microsphere.　Typical　RGB　polymer　film　consisting　gain　materials　are　cladded　on　a　fiber.　To　achieve　single　mode　lasing,　the　polymer　fiber　therein　serves　as　an　excellent　gain　cavity　to　provide　multiple　lasing　modes　while　the　microsphere　acts　as　a　loss　channel　to　suppress　most　of　the　lasing　modes.　Mode　switching　can　be　realized　by　adjusting　the　pump　position.　It　can　be　attributed　to　the　change　of　coupled　efficiency　between　gain　mu-cavity　and　loss　mu-cavity.　Our　work　will　provide　a　platform　for　the　rational　design　of　nanophotonic　devices　and　on-chip　communication.