  Based on the self-consistent scheme beyond mean-field approximation in the
large $N_c$ expansion, including current quark mass explicitly, a general
scheme of SU(2) NJL model is developed. To ensure the quark self-energy
expanded in the proper order of $N_c$, an approximate internal meson propagator
is deduced, which is in order of $O(1/N_c)$. In our scheme, adopting the method
of external momentum expansion, all the Feynman diagrams are calculated in a
unified way by only expanding the quark propagator. Our numerical results show,
that different from the mean field approximation in which the explicitly chiral
symmetry breaking is invisible, the effect of finite pion mass can be seen
clearly when beyond mean-field approximation.
