The thickness deformations of transparent objects can be measured by digital holography,which have been demonstrated in our previous studies.However,the changes of the refractive index caused by the stress in specimens were neglected,which brought errors in measurement.The relation between the phase variation of object wave and the thickness deformation is rebuilt considering the changes of the refractive index,where a new term is introduced for correction.The thickness deformation of a PMMA hole under a uniform tensile force is measured by the experiment.It is proved that the experimental results after correction are in accordance with the theoretical results.Nevertheless the data of thickness deformation calculated by previous relation is larger than the theoretical result.It is known that the correction is right and essential.