The purpose of this article is to construct the nonperturbative expans
ion in quantum chromodynamics using a new small parameter and apply it
to the investigation of the connection between nonperturbative and pe
rturbative regimes of the effective coupling constant. We calculate th
e nonperturbative renormalization group beta-function and discuss the
properties of the series convergence using the two-loop approximation
in this method. Based on the information from meson spectroscopy we de
rive the effective coupling constant in the perturbative region.