  Based on a perturbative approach, we propose a simple and efficient method to
engineer topological edge states in two dimensional magnetic photonic crystals.
The topological edge states in the microstructures can be constructed and
varied by altering the parameters of the microstructure according to the
fieldenergy distributions of the Bloch states at the related Bloch wave
vectors. The validity of the proposed method has been demonstrated by exact
numerical calculations through three concrete examples. Our method makes the
topological edge states 'designable'.
