The interference between virtual photon and 1-- charmonium in e+e- experiment

e+e- experiments producing charmonium are reviewed. It is found that the contribution of the continuum amplitude via virtual photon was neglected in almost all the experiments and the channels analyzed. It is shown that the contribution of the continuum part may affect the final results significantly in ψ(2S) and ψ(3770) decays, while the interference between continuum and resonance amplitudes may even affect the J/ψ decays as well as the ψ(2S) and ψ(3770). This should be considered in analyzing the 'ρπ puzzle' between J/ψ and ψ(2S) decays, and the difference between inclusive hadron and DD-bar cross sections in ψ(3770) decays