  In this article, we calculate the dressed quark propagator with the flat
bottom potential in the framework of the rain-bow Schwinger-Dyson equation.
Then based on the nonperturbative dressed quark propagator, we calculate the
$\pi$ decay constant and the quark condensate. The $\pi$ decay constant is an
important parameter in describing the interplay between dynamical symmetry
breaking and confinement, while the quark condensate is an order parameter for
dynamical chiral symmetry breaking. To implement confinement, we prove that the
dressed quark propagator has no poles on the real timelike $p^2$ axial, the
absence of Kallen-Lehmann spectral representation obviously precludes the
existence of free quarks.
