In this paper, a representation theory in 6-dimensional phase space for Klimonto-vich-Vlasov system is introduced. By using this theory, the relation between the Mis-guich-Balescu's one-particle asymptotic propagator and the Dupree's average Green function is analyzed. It is found that they coincide in the stationary Markovian process, by using them the divergence difficulty of resonance function in the MB's non-linear dispersion relation is resolved. It is pointed out that the divergence difficulty arises from the failure of the concept of fluctuation production operator introduced by MB in their sub-dynamics for the multiple-time-scale perturbation theory.