A metal-loading method (ML) is proposed in this paper to increase effective length, near-field magnitude and radiation efficiency for acoustically actuated piezoelectric antenna (PEA). Field-based circuit model method (FBCM) is utilized to characterize the metal-loaded piezoelectric antenna (MLPEA) by introducing antenna fields into piezoelectric equations and impedance analysis at boundary. Furthermore, current distribution within PE cylinder and on loaded metal rod is calculated by FEM method and formulated with piecewise functions. And, antenna effective length is evaluated with different loaded metal lengths and effects of the loaded metal are analyzed on antenna near-fields and radiation efficiency. All the methods are validated by measurement of a demonstrated MLPEA on a precise testing vehicle with frequency error of 0.05% and near-field magnitude error of 0.97dB. Finally, maximum increase of 4.6dB for near-field magnitude, and 10 times for radiation efficiency is obtained for PEA with loaded metal length of 0.8m. Different loss mechanisms in MLPEA are also analyzed and the radiation efficiency limit for PEA, as estimated by FBCM, is much larger than that of metallic antenna when <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ka</i> is less than 0.1, leaving far more room for radiation efficiency elevation of PEA for the-state-of-art.