  The quantum anomalous Hall (QAH) effect has been recently discovered in
experiment using thin-film topological insulator with ferromagnetic ordering
and strong spin-orbit coupling. Here we investigate the spin degree of freedom
of a QAH insulator and uncover a fundamental phenomenon that the edge states
exhibit topologically stable spin texture in the boundary when a chiral-like
symmetry is present. This result shows that edge states are chiral in both the
orbital and spin degrees of freedom, and the chiral edge spin texture
corresponds to the bulk topological states of the QAH insulator. We also study
the potential applications of the edge spin texture in designing
topological-state-based spin devices which might be applicable to future
spintronic technologies.
