  The development on relativistic nuclear many-body theories is reviewed. The
second order self-energies of hadrons are calculated from $\hat{S}_2$ matrix,
and then an effective method to solve nuclear many-body problems, sum rules on
quantum hadrodynamics, is summarized. The differences between this method and
quantum hadrodynamics are discussed. The effective nucleon mass in the nuclear
matter is redefined in the relativistic Hartree approximation, and a
self-consistent relativistic mean-field model based on quantum hadrodynamics 2
is proposed. It is pointed out that the original definition on effective
nucleon mass in quantum hadrodynamics 2 is not self-consistent, and all the
parameters in the relativistic mean-field approximation should be fixed again
according to the new definition.
