  The Tibet ASgamma experiment just reported their measurement of sub-PeV
diffuse gamma ray emission from the Galactic disk, with the highest energy up
to 957 TeV. These gamma-rays are most likely the hadronic origin by cosmic ray
interaction with interstellar gas in the Galaxy. This measurement provides
direct evidence to the hypothesis that the Galactic cosmic rays can be
accelerated beyond PeV energies. In this work, we try to explain the sub-PeV
diffuse gamma-ray spectrum within cosmic rays diffusive propagation model. We
find there is a tension between the sub-PeV diffuse gamma rays and the local
cosmic ray spectrum. To describe the sub-PeV diffuse gamma-ray flux, it
generally requires larger local cosmic-ray flux than measurement in the knee
region. We further calculate the PeV neutrino flux from the cosmic ray
propagation model. Even all of these sub-PeV diffuse gamma rays originate from
the propagation, the Galactic neutrinos only account for less than ~15% of
observed flux, most of which are still from extragalactic sources.
