  We measure the topological charge of the gauge configurations generated by
lattice simulations of 2 flavors QCD on a $ 16^3 \times 32 $ lattice, with
Optimal Domain-Wall Fermion (ODWF) at $ N_s = 16 $ and plaquette gauge action
at $ \beta = 5.90 $. Using the Adaptive Thick-Restart Lanczos algorithm, we
project the low-lying modes of the 4D effective Dirac operator of ODWF, and
obtain the topological charge and topological susceptibility. Our result of
topological susceptibility agrees with the sea-quark mass dependence predicted
by the chiral perturbation theory, and provides a determination of the chiral
condensate.
