The (Ba0.85Ca0.15) (Ti0.90Zr0.10)O3+xY3++xNb5+(abbreviated as BCZT-x(Nb + Y),x= 0 mol%, 0.05 mol%, 0.1 mol%, 0.2 mol%, 0.3 mol%) lead-free piezoceramics samples were prepared by a traditional solid-state sintering method. And the effects of Yttrium and Niobium elements (Y3+and Nb5+) co-doping on the defect, phase and structure, microstructure, and comprehensive electrical properties have been investigated. Research results show that the Y and Nb elements co-doping can dramatically enhance piezoelectric properties. It is worth noting that XPS defect chemistry analysis, XRD phase analysis and TEM results together show that a new phase of double perovskite structure Barium Yttrium Niobium Oxide (Ba2YNbO6) is formed in the ceramic, and the XRD Rietveld refinement and TEM results show the coexistence of the R-O-T phase. Both these two reasons together lead to significant performance improvements of piezoelectric constant (d33) and planar electro-mechanical coupling coefficient (kp). The functional relation between temperature and dielectric constant testing results present that the Curie temperature increases slightly, which shows the same law as the change of piezoelectric properties. The ceramic sample reaches an optimal performance atx= 0.1% of BCZT-x(Nb + Y), whered33= 667 pC/N,kp= 0.58,εr= 5656, tanδ= 0.022,Pr= 12.8 μC/cm2,EC= 2.17 kV/cm,TC=92 °C, respectively. Therefore, they can be used as potential alternative materials to lead based piezoelectric ceramics.