This paper focuses on the development, process and existing problems of the particle size measuring techniques with the optical means of total scattering. An improved total scattering method has been developed which not only eliminates the ambiguity of the measurements but also offers the size distribution of the particles to be measured. Two calculating methods, i. e. the dependent model and the independent model, are presented. Numerical calculations and computer simulations are also given. The measurements of polystyrene spheres as standard reference material are given at the end of this paper.