  Chaos is usually referred to the sensitivity to initial conditions in which
the nonlinearity plays a crucial role. Beyond such a mathematical description,
the understanding of the underlying physical origin of the chaos is still not
very clear. Here we study the dissipative chaos from the perspective of the
nonequilibrium dynamics. This was not fully investigated in the traditional
chaos theory, despite of the Lorenz's original discovery of chaos from the
nonequilibrium atmosphere. We found that the nonequilibriumness as the degree
of detailed balance breaking can be quantified by the appearance of the steady
state probability flux in the state space. We uncovered that the dynamical
origin of the onset and offset of the dissipative chaos such as Lorentz
attractor is from the sudden appearance and disappearance of such
nonequilibrium flux. We also uncovered that the dissipation associated with the
flux quantified by the entropy production rate gives the thermodynamical origin
of dissipative chaos. The sharp changes in the degree of nonequilibriumness by
the flux and the entropy production rate also provide alternative quantitative
indicators for the onset and offset of the dissipative chaos.
