By using a linear CCD as the detector module, a measuring system for particle size distribution was established by laser diffraction. Based on numerical computation, the two problems in Chin-Shifrin integration particle size inversion algorithm:the divergence of inversion in a small particle size and its false peaks,were analyzed and the causes of these phenomena were explained. Then,the modification of the integration formula was proposed to resolve the divergence problem. Aiming at the particular application on Chin-Shifrin integral transform, the effective angle range of Fraunhofer diffraction approximation to Mie scattering was studied by comparing the pattern of Mie scattering and that of Fraunhofer diffraction.The numerical result show that the valid angle for diffraction approximation decreases as the angle becomes large, but the precision of the inversion has increased. Finally, this improved Chin-Shifrin inversion algorithm was used to process experimental data. The experimental result shows that the improved inversion algorithm has high precision and is suitable for applications in industry.Key words: