In this paper, the main instrument is Quantimet 600 Image Analyzer. By the analysis of the characteristic parameters of slag particle in the images of 2D section, its 3D configuration characteristics can be infered. At the same time, a series of 3D parameters of particle can be obtained, such as particle size distribution, roundness, curve length and curve width, which are gained by the calculation. These parameters were chosen because they directly affect grinding technique, microstructure and property of slag. The results show that: (1) the accumulative weight distribution of slag tallied with Rosin Rammler distribution and amendatory Gauss distribution; (2) the shape factors distribution of slag appears to have good regularities.