In this paper, according to the differences of the index profiles between gradient-index lens and fiber, the focusing method, which was applied successfully in the measurement of fiber and its preform, has been greatly improved on the principle formula and calculating miethod, in order that the focusing method can be suitable to the measurement of gradient lens. The reliability of the modified focusing method was tested by computer simulation and the error of measurement was given in same way. Finally the index profiles of some samples were measnred and compared with fciie results by other method or instrament.