Theoretical expressions of the radiation forces on a dielectric sphere in the Rayleigh regime of light scattering under illumination of a non paraxial laser beam are derived.We show that the single beam trapping produced by a non paraxial Gaussian beam is better than that of a paraxial Guassian beam in two respects,one is that the radiation forces are larger,the other is that there are multi equilibrium positions,which indicate that non paraxial trapping is more suitable in controlling Rayleigh particles.