The magnetic structure，energy band structure and electronic structure of BiFeO3 and BiFe075Co025O3 are investigated by using density functional theory combined with the projector augumented wave （PAW） method. Our numerical results show that the doping of Co does not destroy its perovskite structure and BiFe075Co025O3 keeps the obvious ferroelectricity. The ferromagnetism can be significantly improved since the doping of Co changes the G-type antiferromagnetic order into ferromagneti cone. However，the doping of impurity Co degrades the insulativity.