  The Intermediate Palomar Transient Factory reported the discovery of an
unusual type II-P supernova iPTF14hls. Instead of a ~100-day plateau as
observed for ordinary type II-P supernovae, the light curve of iPTF14hls has at
least five distinct peaks, followed by a steep decline at ~1000 days since
discovery. Until 500 days since discovery, the effective temperature of
iPTF14hls is roughly constant at 5000-6000K . In this paper we propose that
iPTF14hls is likely powered by intermittent fallback accretion. It is found
that the light curve of iPTF14hls can be well fit by the usual t^{-5/3}
accretion law until ~1000 days post discovery when the light curve transitions
to a steep decline. To account for this steep decline, we suggest a power-law
density profile for the late accreted material, rather than the constant
profile as appropriated for the t^{-5/3} accretion law. Detailed modeling
indicates that the total fallback mass is ~0.2M_{sun}, with an ejecta mass
M_{ej}~21M_{sun}. We find the third peak of the light curve cannot be well fit
by the fallback model, indicating that there could be some extra rapid energy
injection. We suggest that this extra energy injection may be a result of a
magnetic outburst if the central object is a neutron star. These results
indicate that the progenitor of iPTF14hls could be a massive red supergiant.
