The trapping force of the optical tweezers is studied using T-matrix method when the particle is in sizes comparable with the wavelength of the incident light.The T-matrix depends only on the composition、size、 shape and orientation of particles, independent of the incident field.The basic principles and the calculation methods of T-matrix method are reviewed.The calculations of trapping force and torque of the single particle and two or more particles using T-matrix method are summarized.The prospect provided by T-matrix method for optical tweezers is also analyzed.