Abstract: Since the establishment of light pen-image analysing system, the per-sonnel involved in rock and mineral analysis have been extricated from large amount of statistical and complex computation, and the efficiency and quality of the measurement of particle size have been greatly improved. In order to extend the range of application of the method, and to provide more data for petrofabric, the following problems a e discussed. Operational principles of the instrument; Noticeable problems during testing; Usage of the program of line-section percentage; Case study of the application.