Defect greatly affects the microscopic structure and electrical properties of perovskite piezoelectric ceramics, but the microscopic mechanism of defect-driven macroscopic properties in the materials is not still completely comprehended. In this work, K0.5Na0.5NbO3+x mol CuSb2O6 lead-free piezoelectric ceramics were fabricated by a solid-state reaction method and the defect-driven evolution of piezoelectric and ferroelectric properties was studied. The addition of CuSb2O6 induces the formation of dimeric (Cu-Nb(''') - V-O(center dot center dot))' ( DC1) and trimeric dV(O)(center dot center dot) - Cu-Nb(''') - V-O(center dot center dot))(center dot) (DC2) defect dipoles. At low doping concentration of CuSb2O6 (0.5-1.0 mol%), DC1 and DC2 coexist in the ceramics and harden the ceramics, inducing a constricted double P-E loop and high Q(m) of 895 at x= 0.01. However, DC2 becomes more dominant in the ceramics with high concentration of CuSb2O6 (>= 1.5 mol%) and thus leads to softening behavior of piezoelectricity and ferroelectricity as compared to the ceramic with x= 0.01, giving a single slanted P-E loop and relatively low Q(m) of 206 at x= 0.025. All ceramics exhibit relatively high d(33) of 106-126 pC/N. Our study shows that the piezoelectricity and ferroelectricity of K0.5Na0.5NbO3 ceramics can be tailored by controlling defect structure of the materials.