  We have constrained the intrinsic parameters, such as the magnetic energy
density fraction ($\epsilon_{B}$), the electron energy density fraction
($\epsilon_e$), the initial Lorentz factor ($\Gamma_0$) and the Lorentz factor
of the reverse external shock ($\Gamma_{rs}$), of GRB990123, in terms of the
afterglow information (forward shock model) and the optical flash information
(reverse shock model). Our result shows: 1) the inferred values of $\epsilon_e$
and $\epsilon_B$ are consistent with the suggestion that they may be universal
parameters, comparing to those inferred for GRB970508; 2) the reverse external
shock may have become relativistic before it passed through the ejecta shell.
Other instrinsic parameters of GRB990123, such as energy contained in the
forward shock $E$ and the ambient density $n$ are also determined and discussed
in this paper.
