Abstract: The acoustic scattering characteristics of polymethyl methacrylate (PMMA) material are different from those of metal materials. Since the phase velocity of Rayleigh wave in PMMA material is less than the sound speed in water, the scattering mechanism needs to be re-examined. The target strengths of the PMMA sphere and the steel sphere with the same size in water are compared based on the normal series solution of the elastic sphere scattering sound field. It is found that the former exhibits higher target strength at low frequencies. Based on the acoustic tunneling effect of subsonic wave and the resonance characteristics of surface surround wave propagation, the physical mechanism of the target strength enhancement at low frequencies caused by subsonic Rayleigh wave in PMMA sphere is explained and analyzed. Finally, the acoustic scattering experiments of PMMA sphere and steel sphere are carried out to verify the accuracy of the analysis results.