Interaction between dislocation and defect induced by X-irradiation has been investigated in NaCl and KCl single crystals by strain rate cycling tests under superimposition of ultrasonic oscillation during plastic deformation. The interaction energy between dislocation and radiation-induced defect has been obtained by fitting Barnett model to experimental results, assuming that the defect is tetragonal. The interaction energies between dislocation and defect were determined to be 0.39 and 0.87eV for NaCl and KCl, respectively. The larger interaction energy for KCl presents its larger tetragonality of defect induced by X-irradiation than NaCl.