A simplified model of one dimensional elastic dipole discrete lattice containing oscillating dislocations is proposed to study the nonlinear stress-induced diffusion of interstitials in the inhomogeneous stress field of dislocation and to set up a foundation for further numerical calculation in real crystals, consequently, to clarify the interaction of the external stress, the dislocations and the octahedral interstitials in bcc crystals and to explain S-K relaxation and the effect of dislocation on Snoek relaxation theoretically. The simulation computation shows that the nonlinear diffusion of interstitials induced by the dislocation stress field makes the interstitials form a Fermi-Dirac distrubution of defects and enhances Snoek effect, hence, a peak of Snoek effect of nonlinear diffusion appears at higher temperature than that of Snoek peak.