Abstract: Traditional range migration (RM) algorithms are based on the assumption of a homogeneous medium, making them unsuitable for layered medium scenarios in ground penetrating radar (GPR) applications. Moreover, accurately obtaining the migration velocity model in practical applications faces significant challenges. To address these issues, a layered medium RM imaging algorithm based on self-focusing technology for GPR is proposed in this paper. The algorithm adopts wavefield phase continuation in the frequency-wavenumber domain to handle electromagnetic wave path bending at layered interfaces, extrapolating the wavefield from the upper medium to each layer boundary, followed by layer RM imaging to achieve precise focusing of target energy in layered medium. On this basis, a self-focusing technique is introduced to estimate the relative permittivity of the detection region by comprehensively utilizing four evaluation metrics: image entropy, contrast, higher-order moments, and average intensity measure, thereby obtaining an accurate migration velocity model and improving imaging precision. Results of simulation and measurement demonstrate that the proposed method achieves accurate relocation of target reflected waves and clear energy focusing in layered medium scenarios, and has distinct advantages in both relative permittivity estimation accuracy and layered medium imaging precision.