In this paper, we investigate the effect of the boundary of the nonlocal nonlinear medium on the propagation of soliton. On the basic of NNLSE and the Poisson equation, using the Green function approach, we obtain the response function of the lead glass of finite-size, which is a strong nonlocal medium. Starting with the paraxial ray equation, we obtain the analytical solutions of the oscillation trajectory and period of the beam. Comparing the analytical solutions with numerical simulations, we found that our analytical solutions are precise when the point of incidence is not near the boundary of the medium.