Abstract: In this paper,after putting forward the principle of LSST in detecting micro bulk defects in silicon and some simulating results of various size of defects scattering distributions,a novel analyzing way called character recognition is developed.This paper presents the first character defined according to wave number of the laser scattering distribution,and the second character defined according to the unsymmetry of scattering optical intensity.By using the character Ⅰ,the quantity scale of bulk defects can be obtained first,and then with character Ⅱ the detailed quantity scale less than 1μm can be gained if the character Ⅰ is 1.The method has the advantages of analyzing defects size quickly and making it possible to implement automation of detecting system,etc.It is worth being used in practice.