K2Ba3Si8O20:Eu2+ as a new green-emitting phosphor was prepared and studied in this article. This material showed powerful absorption in near ultraviolet-visible regions from 350 to 450 and its green-emitting band peaked at 502 nm. Its photoluminescence emitting intensity affected by concentrations of K2Ba3Si8O20:Ce3+ and K2Ba3Si8O20:Eu2+ was also studied and consequently verified to be a dipole dipole interaction. Effective energy transfer was observed in Ce3+,Eu2+ co-doped K2Ba3Si8O20 phosphor, and the transfer efficiency was also obtained from the decay lifetime. The K2Ba3Si8O20:Eu2+ phosphor combined with a 380 nm near-UV chip was demonstrated to produce a diode which emitted green light. This article indicates that the phosphor prepared in this work could be used in manufacturing of white light-emitting diodes.