Adopting Lorentz-invariant coupling model of neutron n-antineutron n and neutral meson strong interaction, we made physical analysis and accurate calculation of the n-n renormalization chain diagram propagator, and obtained the theoretical results. Furthermore, in applying it to the physical process analysis and cross-section evaluation in the reaction n+n→2π0, its differential cross-section is obtained. Through the comparison between this calculation and those scenarios, namely the n-n tree diagram and renormalization chain diagram propagator contribution, some important information about radiative correction was obtained. This study would offer certain academic references to the further research on Lorentz-invariant coupling model and the nuclear physics about cross section problem of particles in nucleon antinucleon and neutral meson strong interaction in terms of theoretical calculations. In addition, it will also provide something valuable on relevant physical processes, and on the renormalization calculation orderly with different approaches in perturbation theory of quantum field theory.