This paper deals with the acoustic absorbing ability affected by the amount and attenuation coefficient of perfectly-matched layers（PML） in acoustic finite-difference time-domain（FDTD） method,and establishes a PML boundary model for the absorbing ability analysis.The results indicate that（1） the layer amount and the attenuation coefficient relate to each other;（2） more PML layers may result in high absorbing ability but heavy computation burden;（3） when the layer amount is unchanged,appropriate attenuation coefficient should be set for each attenuation layer for the purpose of decreasing the numerical reflection due to the difference in attenuation coefficient;and（4） in practical applications,suitable layer amount and attenuation coefficient should be determined by comprehensively considering the calculation complexity and accuracy.