  We propose that CaP3 family of materials, which include CaP3, CaAs3, SrP3,
SrAs3 and BaAs3 can host a three-dimensional topological nodal line semimetal
states. Based on first-principle calculations and kp model analysis, we show
that a closed topological nodal line exists near the Fermi energy, which is
protected by the coexistence of time-reversal and spatial inversion symmetry
when the band inversion happens. A drumhead-like surface states are also
obtained on the c-direction surface of these materials.
