To measure the radius of microsphere particles effectively, economically and accurately,the Mie scattering theory is adopted to design the radius measuring device.The theoretical analysis and numerical calculations of microsphere particle light scattering characteristics are carrying out by using Mie scattering theory.Moreover, the relations of the distribution of scattering light and incident wavelength, the radius of microparticle and the relative index of the microsphere particle are presented. Three results are obtained.Firstly, the energy of scattering light distributes in the area where scattering angle is small when the incident wavelength is small.Secondly, the variety of the relative index has little effect on the distribution of scattering light.Thirdly, the distributions of scattering light have great difference according to different radiuses of microsphere particle,so that the radius of the microsphere particle could be obtained by measuring the distribution of the scattering light,therefore,the feasibility of the design scheme is proved theoretically.The radius measuring device for microsphere particles is designed based on theoretical analysis and numerical calculations.The device has the merits of simple structure,low cost and high efficiency.The device is practical and could be adapted to practical measurement.