The optical tweezers is widely used in many biological applications.Despite the apparent simplicity of a laser trap,a single particle is trapped with a single beam,exact calculation of the optical forces on particles is very difficult.Calculations can be performed by using some approximate methods such as Ray-Optics and Raleigh hypothesis,but these are only applicable within their ranges of validity.We can obtain a general theory for laser trapping by applying the electromagnetic scattering theory.In this paper, we describe how the T-matrix approach can be used to computer optical trapping force.According to the simulation results,we can easily choose parameters of the trapping system.