With growing concerns over environmental protection, lead-free dielectric ceramic capacitors are attracting much attention. In this work, a series of novel (1-x) Na0.5Bi0.5TiO3-x Ba5LaTi3Ta7O30 ((1-x)NBT-xBLTT) dielectric composite ceramics were fabricated by a traditional solid‐state method. All the samples possess a compact microstructure with refined grain morphology with increasing BLTT content, and tend to exhibit a diphase dielectric composite as x reaches up to 0.05. Furthermore, the addition of BLTT enhances the dielectric relaxor behavior of NBT-based ceramics, such that the x = 0.15 composite ceramic exhibits a typical feature of relaxor ferroelectrics. As a result, a high recoverable energy-storage density of Wrec~3.67 J/cm3, an ultrahigh energy-storage efficiency of η~97.3%, and a high power density of PD~333 MW/cm3 can be simultaneously obtained in the x = 0.15 relaxor composite ceramic. This study provides an alternative way to design excellent energy-storage performances in NBT-based compositions through constructing dielectric relaxor composites via introducing non-polar tungsten bronze oxides.