  We study the topological edge states of the Haldane's graphene model with
zigzag/armchair lattice edges. The Harper equation for solving the energies of
the edge states is derived. The results show that there are two edge states in
the bulk energy gap, corresponding to the two zero points of the Bloch function
on the complex-energy Riemann surface. The edge-state energy loops move around
the hole of the Riemann surface in appropriate system parameter regimes. The
quantized Hall conductance can be expressed by the winding numbers of the edge
states, which reflects the topological feature of the Haldane model.
