  We study the arc statistics of gravitational lensing generated by dark matter
halos in order to probe their density profile. We characterize the halo profile
by two parameters, the inner slope of the central cusp $\alpha$, and the median
amplitude of the concentration parameter, $c_{\rm norm}$, for a halo of mass
$10^{14}h^{-1}M_\odot$ at $z=0$, and compute the numbers of tangential and
radial arcs produced by gravitational lensing of galaxy clusters. We find that
the number of arcs divided by the number of halos is a good statistic which is
sensitive to both $c_{\rm norm}$ and $\alpha$ with very weak dependence on the
cosmological parameters. If the arc samples with well-defined selection
criteria for the clusters become available, one can strongly constrain both
$c_{\rm norm}$ and $\alpha$. While our tentative comparison with the existing
observational data indicates that the inner density profile of dark halos is
indeed as steep as predicted by recent simulations ($\alpha \sim 1.5$), the
homogeneous samples of tangential and radial arcs are required for more
quantitative discussions.
