  An integrable Kondo lattice model, which describes a strongly correlated
electron host interacting with a spin-1/2 lattice, is proposed. It is found
that with the variations of the Kondo coupling J, the hole concentration n_h
and the magnetic field H, the system may fall into a variety of phases. The
phase boundaries of the ground state are determined exactly. The marginal
excitations and the quantum critical behavior at the phase boundaries are
discussed.
