  The recent observations by pulsar timing array (PTA) experiments suggest the
existence of stochastic gravitational wave background in the nano-Hz range. It
can be a hint for the new physics and cosmic string is one of the promising
candidate. In this paper, we study the implication of the PTA result for cosmic
strings and dark photon dark matter produced by the decay of cosmic string
loops. It can simultaneously explain the PTA result and present dark matter
abundance for the dark photon mass m~10^{-6}--10^{-4}eV. Implications for the
gravitational wave detection with multi-frequency bands are also discussed.
