  The decay mode $\psi(2S)\to J/\psi+\gamma\gamma$ is proposed in order to
experimentally identify the effects of the coupling of charmonium states to the
continuum $D\bar D$ states. To have a better understanding of such a two-photon
decay process, in this work we restrict ourselves to investigate the
contribution of the discrete part, in which the photons are mainly produced via
the intermediate states $\chi_{cJ}(nP)$. Besides calculating the resonance
contributions of $\chi_{cJ}(1P)\; (J=0,1,2)$, we also take into account the
contributions of the higher excited states $\chi_{cJ}(2P)$ and the interference
effect among the 1P and 2P states. We find that the contribution of the 2P
states and the interference terms to the total decay width is very tiny.
However, for specific regions of the Dalitz plot, off the resonance peaks, we
find that these contributions are sizable and should also be accounted for. We
also provide the photon spectrum and study the polarization of $J/\psi$.
