  Topological nodal-line semimetals (TNLSMs) are materials whose conduction and
valence bands cross each other, meeting a topologically-protected closed loop
rather than discrete points in the Brillouin zone (BZ). The anticipated
properties for TNLSMs include drumhead-like nearly flat surface states, unique
Landau energy levels, special collective modes, long-range Coulomb
interactions, or the possibility of realizing high-temperature
superconductivity. Recently, SrAs3 has been theoretically proposed and then
experimentally confirmed to be a TNLSM. Here, we report high-pressure
experiments on SrAs3, identifying a Lifshitz transition below 1 GPa and a
superconducting transition accompanied by a structural phase transition above
20 GPa. A topological crystalline insulator (TCI) state is revealed by means of
density functional theory (DFT) calculations on the emergent high-pressure
phase. As the counterpart of topological insulators, TCIs possess metallic
boundary states protected by crystal symmetry, rather than time reversal. In
consideration of topological surface states (TSSs) and helical spin texture
observed in the high-pressure state of SrAs3, the superconducting state may be
induced in the surface states, and is most likely topologically nontrivial,
making pressurized SrAs3 a strong candidate for topological superconductor.
