By decomposing the Bogomol yi self-dual equation in the Abelian Che-Simons Higgs model, we find a selfdual topological term that was ignored all the time in the Bogomol yi self-duality equation due to the improper decomposition of the complex Higgs field. We also present a new self-dual equation that includes the topological term. It is shown that the self-dual vortex just arises from the symmetric phase of the Higgs field φ = 0. Using our φ-mapping theory, the inner topological structure of the vortex and double vortex is given.