The temperature dependence of the resistivity of an epitaxial YBa2Cu3O7-δ thin film has been measured in various magnetic fields up to 7T applied parallel to the c-axis near Tc. The result shows that the resistivity below Tc can be well fitted by thermally activation flux motion. The current density dependence of the effective pinning potential follows a logarithmic law proposed by Zeldov et al. The temperature and magnetic field dependence of the effective pinning potential follows U(H,T)=U0(1-T/Tc)H-α, with α=0.63, showing 2D behavior, It is consistent with the plastic deformation model of the flux-line lattice at flux-line-lattice dislocations.