A new oxide NaCu3Fe2Os2O12 is synthesized using high pressure and temperature conditions. The Rietveld structural analysis shows that the compound possesses both A- and B-site ordered quadruple perovskite structure in Pn (3) over bar symmetry. The valence states of transition metals are confirmed to be Cu2+/Fe3+/Os5.5+. The three transition metals all take part in magnetic interactions and generate strong Cu2+(up arrow)Fe3+(up arrow)Os5.5+(down arrow) ferrimagnetic superexchange interactions with a high Curie temperature about 380 K. Electrical transport measurements suggest its half-metallic properties. The first-principles theoretical calculations demonstrate that the compound has a spin-down conducting band and a spin-up insulating band with a wide energy gap.