  A universal mechanism to generate chiral hinge states in the ferromagnetic
axion insulator phase is proposed, which leads to an exotic transport
phenomena, the quantum anomalous Hall effect (QAHE) on some particular surfaces
determined by both the crystalline symmetry and the magnetization direction. A
realistic material system Sm doped $\text{Bi}_2\text{Se}_3$ is then proposed to
realize such exotic hinge states by combing the first principle calculations
and the Green's function techniques. A physically accessible way to manipulate
the surface QAHE is also proposed, which makes it very different from the QAHE
in ordinary 2D systems.
