Recently, the finite difference time domain (FDTD) method has been frequently used for the analysis of underwater sound propagation. There are demonstrated advantages of this FDTD method in terms of obtaining data regarding snapshots of sound pressure distribution and a series of waveforms at any point. In addition, the method facilitates the modeling of factors, such as the sound source and media into the analysis domain. In this study, a three-dimensional FDTD analysis was carried out in order to obtain the sound field focused by a biconcave acoustic lens specialized to measure the normal incidence of the spherical wave. Additionally, the results of the analysis were compared with experimental results obtained in a water tank. When the frequency of the sound source was 500 kHz, the range between the acoustic lens and the sound source was 1.78 m, and the attenuation constant was 0.5–1.0 dB/λ, the experimental results regarding the position of the focal point, the on-axis characteristics and the beam pattern were all found to agree well with the simulation results obtained by FDTD method.