In order to accurately and simply calculate the acoustic radiation force,the FDTD (Finite Difference Time Domain) method is applied to discrete the acoustic wave equations in both spatial and temporal domain. By setting the appropriate boundary conditions, the pressure and velocity are computed by numerical iteration in time domain. The two-dimensional acoustic radiation force on a rigid spherical particle in water is calculated by the momentum-flux tensor equations and the finite difference domain method. The influence of frequence and shift distance from beam center on acoustic radiation force are obtained for rigid sphere particle.The results show that the axial acoustic radiation force decreases with the axial shift distance. When the particle is moved away from the beam axial, the axial acoustic radiation force is reduced. The transverse radiation force is increasing first then decreasing as the shift distance increased.The directions of the transverse force are opposite and the amplitudes of them are same when the particle shifts from the beam center with same distance.

FDTD; Gaussian beam; off-axial acoustic radiation force; numerical simulation