The 99.7K0.5Na0.5(Nb(1-x)Tax)O3-0.3BaBiO3 lead-free piezoelectric single crystals of tantalum pentoxide and manganese dioxide doped were prepared by a seed-free solid-state crystal growth method, and the effects of mono-doping and co-doping of Ta and Mn on the growth, structure and electrical properties of the crystals were investigated. The result shows that a proper amount of Ta and Mn co-doping is beneficial to the growth of the single crystal. The single crystal surface becomes more regular and compact, and the maximum size of the obtained crystal can reach 30.0 mm×9.2 mm×2.6 mm when 0.9% (mole fraction) Ta and 0.1% Mn are co-doped. When 0.1% Mn doping is fixed and the amount of Ta is changed, the single crystals with a greater amount of tantalum pentoxide doping have higher piezoelectric properties. When the co-doping amounts of Ta and Mn are 0.9% and 0.1%, the crystals have greater remanent polarization (i.e., Pr = 26.96 μC/cm2) and piezoelectric constant (i.e., d33 = 227 pC/N), respectively.