  Following the method of Victor V. Kozlov et al.[PhysRevA. 74. 063829],we
inspect the coherence induced by incoherent pump and spontaneous decay process
in $\Lambda$ type three-level atomic system with degenerated lower duplicate
levels. The system shows a coherent population trapping state and multi-steady
states characteristic in different conditions. Interestingly, two kinds of
steady states generated by the system in different sets of pumping and decaying
parameters, the "singlet" state and the "triplet" state, exhibit stable or
unstable characteristics under the action of pumping field and vacuum
reservoir, which promise fruitful applications to atomic coherence and
interference in quantum optics.
