Abstract: Based on Frunhofer-diffraction, the diffraction intensities of lognormal distribution particles is numerically culculated in this paper. It is displayed in figures as a function of diffraction angle for the different number-size and wight-size distribution parameters. Influnce of the dispersity and medium particle diameter on the central intensity of diffraction pattern and production, the number, and the position angle of diffraction fringe are introduced by comparing and analysing.