In this work, novel lead-free relaxor ferroelectric (1-x)［0.9BaTiO3-0.1Bi(Mg0.25Ta0.5)O3］-xBi0.5Na0.5TiO3ceramics were synthesized via composite strategy using the traditional solid-state process. Results indicate that the incorporation of Bi0.5Na0.5TiO3 with a high Curie temperature could not only significantly enhance the energy storage density, but also improve the temperature stability. As BNT concentration rose, the nano-scale polarization mismatch dominated by Bi-O coupling was established and enhanced, significantly compensating for the reduction of macroscopic polarization due to the addition of Bi(Mg0.25Ta0.5)O3, leading to elevate saturation polarization and improve temperature stability. The ceramics which x is 0.2 show optimal energy storage features with a high energy storage density of 4.01 J/cm3 in the electric field of 245 kV/cm combined with a relatively high energy storage efficiency of 84.86%. Moreover, excellent temperature stabilities were noticed with the change rate of energy storage density is less than 5% and energy storage efficiency is less than 6% over a broad temperature range (20~170 ℃).