  This paper briefly summarizes the status of the cosmic ray observations by
EAS (Extended Air Shower) experiments with energy below 10**16eV and the
related studies of the hadronic interaction models. Based on the observed sharp
knee structure and the irregularities of the cosmic ray spectrum around knee
energy, plus the newly discovered electron and positron excess, the origin of
the galactic cosmic rays and the single source model interpretation are
discussed, but convincing evidence is not yet available. High precision
measurements of the mass composition of primary cosmic rays at knee energy will
be very useful to disentangle the problem. To reach this goal, a better
understanding of the hadronic interaction models is crucial. It is good to see
that more dedicated accelerator and cosmic ray experiments will be conducted
soon. As one EAS component, the muon distribution and muon charge ratio are
important for testing the hadronic interaction models. In addition muons are an
important background to neutrino experiments and all underground ultra-low
background experiments. They are also a very useful tool for the meteorological
studies.
