We investigated the possible candidates of half-metal (HM) material in double perovskites structure Sr2BB′O6 (B, B′=3d transition metal). The electronic structure calculations were based on density functional theory (DFT) with both generalized gradient approximation (GGA) and GGA+U approaches, where +U is on-site Coulomb interaction correction. With the consideration of 4 types of magnetic states, i.e. ferromagnetic (FM), ferromagnetic (FiM), antimagnetic (AF) and nonmagnetic (NM), we found 5 promising candidates for half-metallic (HM) materials: Sr2ScCrO6, Sr2TiCrO6, Sr2MnCrO6, Sr2ZnMnO6 and Sr2ZnFeO6.