  With the successful launch of the Swift Gamma-Ray Burst Explorer, people
expected the prompt optical flash like GRB990123 would be easily detected.
However the fact that early optical flash have not been detected for a number
of GRBs indicates the reverse shock must be suppressed. Here we explore the
possibility that the optical flash may arise from the internal shock. We find
that, under certain circumstance, the optical flash of GRB990123 and GRB060111b
can really be explained by the internal shock. For GRB041219a, the prompt
optical emission was correlated with the gamma-ray emission, we explain this
feature also in the internal shock scenario, the optical emission is the low
energy extension of the gamma-ray emission, and we can restrict its redshift
$z\sim 0.2$. As for GRB050904, we have shown in previous paper that the optical
flash was produced by synchrotron radiation and the X-ray flare was produced by
the synchrotron-self-Compton mechanism. Therefore we conclude that the early
optical flash of GRBs can usually come from the internal shock. Meanwhile since
the condition to produce the optical flash is not easily satisfied, so the
optical flash like GRB990123 should not be common in GRBs. In addition, we also
discussed the synchrotron-self-Compton effect in the internal shock model, and
find that for different values of parameters, there would be soft gamma-ray
(100 KeV), hard gamma-ray (10 MeV) and GeV flare accompanying the optical
flash. For GRB like GRB990123, a GeV flare with fluence about 10^{-8} erg
cm^{-2} s^{-1} is expected, which may be detected by the GLAST satellite.
