A series of lead-free dielectric energy storage ceramics BNT-BT-KNN with a composition ratio of 0.94Bi0.5Na0.5TiO3-(0.06-x)BaTiO3-xK0.5Na0.5NbO3(BNT-BT+xKNN, x=0.00~0.04) were prepared by solid state reaction method. The effect of KNN doping on the crystal structure, micro-structure, dielectric, ferroelectric properties and energy storage efficiency of BNT-BT-based ceramic was investigated. The results show that all the samples exhibit the pure perovskite structure with uniform and dense grains in the medium after sintering at 1 150 ℃. The addition of KNN further broadens the dielectric peak at Tm which resulted in better temperature stability and relaxation. With the increase of KNN dopant, the hysteresis curves (P-E curves) of the samples gradually change from “broad and fat” to “slender” and the residual polarization (Pr) of the ceramic samples decrease, thus the energy storage performance of BNT-BT ceramics are further improved. The optimal energy storage density of Wrec=0.048 J/cm3 was achieved at x=0.03 under a field strength of 2 kV/mm, which corresponds to an energy storage efficiency of η=43%, which proves that this material has a promising potential for application in energy storage capacitors.