  We examine the topological properties of a spin-singlet superconductor with
Rashba and Dresselhaus (110) spin-orbit couplings. We demonstrate that there
are several topological invariants in the Bogoliubov-de Gennes (BdG)
Hamiltonian by symmetry analysis. We use the Pfaffian invariant $\mathcal{P}$
for the particle-hole symmetry to demonstrate all the possible phase diagrams
of the BdG Hamiltonian. We find that the edge spectrum is either Dirac cone or
flat band which supports the emergence of the Majorana fermion in this system.
For the Majorana flat bands, a higher symmetric BdG Hamiltonian is needed to
make them topologically stable. The Pfaffian invariant $\mathcal{P}(k_{y})$ and
the winding number $\mathcal{W}(k_{y})$ are used in determining the location of
the Majorana flat bands.
