Analysis of glass homogeneity using the attaching interferometric data model neglects body distribution. To improve analysis accuracy, we establish the three-dimensional gradient index (GRIN) model of glass index by analyzing fused silica homogeneity distribution in two perpendicular measurement directions. Using the GRIN model, a lithography projection lens with a numerical aperture of 0.75 is analyzed. Root mean square wavefront aberration deteriorates from 0.9 to 9.65 nm and then improves to 5.9 nm after clocking.