A series of Eu- and Gd-coactivated SrB4O7 phosphors was synthesized, and the energy transfer between Eu2+-Gd3+-Eu3+ was observed and investigated. We monitored that energy transfer from Eu2+ to Eu3+ through Gd3+ via a direct observation and analysis about decay lifetimes and the significant spectra overlap of Eu2+ and Eu3+, which are also in accord with the result from concentration quenching methods. When co-doping with a certain amount of Gd3+, energy can be converged on Eu3+, and the photoluminescence of SrB4O7:Eu is changed prominently. This research about the energy transfer of SrB4O7:Eu,Gd exhibits great potential for the development of red-emission phosphors.