  High energy emission (> tens MeV) of Gamma-Ray Bursts (GRBs) provides an
important clue to understand the physical processes involved in GRBs, which may
be correlated with the GRB early afterglow. A shallow decline phase has been
well detected in about half {\it Swift} Gamma-ray Burst X-ray afterglows. The
widely considered interpretation involves a significant energy injection and
possibly time-evolving shock parameter(s). This work we calculate the
synchrotron-self-Compton (SSC) radiation of such an external forward shock and
show that it could explain the well-known long term high energy (i.e., tens MeV
to GeV) afterglow of GRB 940217. We propose that the cooperation of Swift and
GLAST will help to reveal the nature of GRBs.
