  We perform lattice simulations of two flavors QCD using the optimal
domain-wall fermion, in which the chiral symmetry is preserved to a good
precision ($ m_{res} \sim 0.3 $ MeV) on the $ 16^3 \times 32 $ lattice ($ L
\sim 2 $ fm) with inverse lattice spacing $ a^{-1} \sim 1.8 $ GeV, and $ N_s =
16 $ in the fifth dimension, for eight sea quark masses corresponding to the
pion masses in the range 210-500 MeV. We present our first results of the mass
and the decay constant of the pseudoscalar meson, which are in good agreement
with the next-to-leading order chiral perturbation theory for $ M_\pi < 450 $
MeV, and from which we determine the low-energy constants $ f $, $ \Sigma $, $
\bar{l}_3 $ and $ \bar{l}_4 $. At the physical pion mass $ M_{\pi} = 135$ MeV,
we obtain the pion decay constant $f_\pi =133(1)(2)$ MeV, and the average up
and down quark mass $m_{ud}^{\bar{\rm MS}}(\mathrm{2 GeV})=4.09(7)(11)$ MeV,
where the first error is statistical, and the second error is systematic due to
the truncation of the higher order corrections and the uncertainty in the
determination of the lattice spacing. Furthermore, we also obtain the chiral
condensate $ \Sigma^{\bar{{\mathrm{MS}}}}(2 GeV) = [250(4)(7) MeV]^3 $.
