  Kramers' theorem ensures double degeneracy in the energy spectrum of a
time-reversal symmetric fermionic system with half-integer total spin. Here we
are now trying to go beyond the closed system and discuss Kramers' degeneracy
in open systems out of equilibrium. In this letter, we prove that the Kramers'
degeneracy in interacting fermionic systems is equivalent to the degeneracy in
the spectra of different spins together with the vanishing of the inter-spin
spectrum. We find the violation of Kramers' degeneracy in time-reversal
symmetric open quantum systems is locked with whether the system reaches
thermal equilibrium. After a sudden coupling to an environment in a
time-reversal symmetry preserving way, the Kramers doublet experiences an
energy splitting at a short time and then a recovery process. We verified the
violation and revival of Kramers' degeneracy in a concrete model of interacting
fermions and we find Kramers' degeneracy is restored after the local
thermalization time. By contrast, for time-reversal symmetry $\tilde{\cal T}$
with $\tilde{\cal T}^2=1$, we find although there is a violation and revival of
spectral degeneracy for different spins, the inter-spin spectral function is
always nonzero. We also prove that the degeneracy in spectral function
protected by unitary symmetry can be maintained always.
