The equilibrium geometries, electronic structures and UV-vis spectra of a series of spiroannelated quinone-type methanofullerenes have been determined by using Zerner’s intermediate neglect of differential overlap method. The results show that between fullerene and the addend there exists a special interaction, “periconjugation”, which results in through-space orbital interactions. The calculated UV-vis spectra are in good agreement with experiments. On the basis of the electronic spectra, the β values are calculated. The results show that spiroannelated quinone-type methanofullerenes have quite large β values. We attribute the large β values to both the charge transfer from C60 to benzoquinone and on the C60 three-dimensional conjugated sphere.