1. A method for measuring and analyzing particle size distribution, the method comprising: collecting an analyzing particle size distribution of a given sample content from a particle size measuring instrument; setting up an estimated particle size distribution as a theoretical distribution based upon portions of distributions for the given sample content particle size distribution; comparing between the analyzing particle size distribution and the estimated particle size distribution so as to determine the difference therebetween; and making the difference a characteristic parameter for classifying the analyzing particle size distribution according to the sample content.