In the process of manufacturing square GRIN lens,ion-exchanging to cylindrical glass stick Tl was made by ion-exchange method at first,then square GRIN lens sample was machined. The refractive index distribution was measured by Ya-Ming interferometer method,and the aberration was measured by foursquare grid chart. The measurement results were compared with that of related reference. The results show that square GRIN lens sample manufactured by this work has smaller aberration and better imaging quality. But the maximal value of refractive index distribution is deviated from the geometric central axis of the square GRIN lens,while that is not existed in related reference. The results of this research have certain reference value and guiding significance for the development of square GRIN lens.