  Exploring new unconventional superconductors is of great value for both
fundamental research and practical applications. It is a long-term challenge to
develop and study more hole-doped superconductors in 1111 system of iron-based
superconductors. However, fifteen years after the discovery of iron-based
superconductors, it has become increasingly difficult to discover new members
in this system by conventional means. Here we report the discovery of
superconductivity with the critical transition temperature up to 30.7 K in the
parent compound CaFeAsF by an annealing treatment in air atmosphere. The
superconducting behaviors are verified in both the single-crystalline and
polycrystalline samples by the resistance and magnetization measurements. The
analysis by combining the depth-resolved time-of-flight secondary ion mass
spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) measurements
show that the introduction of oxygen elements and the consequent changing in Fe
valence by the annealing treatment may lead to the hole-type doping, which is
the origin for the occurrence of superconductivity. Our results provide a new
route to induce hole-doped superconductivity in Fe-based superconductors.
