Because the diameter of the trapped sphere obtained by the optical tweezer usually locates in the intermediate range, theoretical calculation was difficult. OTT1 optical tweezers computational toolbox is a kind of T matrix method based on the GLMT theory. The development of the OTT1 optical tweezers computational toolbox makes detailed calculation and evaluation feasible. In this paper, the optical trapping coefficiency curve, its linearity and stiffness, and the interchangebility of Duke series polystyrene sphere were calculated and evaluated. The results show that when the numerical aperture becomes closer to the refractive index of water, a better trapping effect will be achieved; when an 800~1 200 nm polystyrene sphere is trapped, the stiffness of optical tweezers is larger; when a PS sphere with diameter smaller than 2 000 nm is used, the linearity of optical tweezers is better; when Duke series sphere with a 800~2 000 nm diameter is adopted, the interchangeability between the same series spheres is better, which will be convenient to calibrate the nanometer optical tweezers; for avoiding Mie resonance, the sphere diameter should be smaller than 2 500 nm.