  The new discovered iron-based superconductors have chain-like As layers.
These layers generate an additional 3-dimensional hole pocket and cone-like
electron pockets. The former is attributed to the Ca $d$ and As1 $p_z$ orbitals
and the latter are attributed to the anisotropic Dirac cone, contributed by As1
$p_x$ and $p_y$ orbitals. We find that large gaps on these pockets open in the
collinear antiferromagnetic ground state of CaFeAs$_2$, suggesting that the
chain-like As layers are strongly coupled to FeAs layers. Moreover due to the
low symmetry crystal induced by the As layers, the bands attributed to FeAs
layers in $k_y=\pi$ plane are two-fold degenerate but in $k_x=\pi$ plane are
lifted. This degeneracy is protected by a hidden symmetry
$\hat{\Upsilon}=\hat{T}\hat{R}_y$. Ignoring the electron cones, the materials
can be well described by a six-band model, including five Fe $d$ and As1 $p_z$
orbitals. We suggest that these new features may help us to identify the sign
change and pairing symmetry in iron based superconductors.
