(Bi0.5Na0.5)Ti1-xCoxO3 ( 0≤x≤0.015) lead free piezoceramics were prepared by the conventional solid phase method. All the BNT specimens presented a monoclinic phase of Cc in crystal structure and the addition of Co caused a remarkably promoted grain growth. Simultaneously, Co cation enters into the B-site of the perovskite lattice, forming the hard doping effect, the oxygen vacancies in the lattice are generated, the internal bias field of BNT increased, and the temperature stabilization of BNT ferroelectricity is improved.