Abstract: Lateral confined compression tests for saturated crushed limestone were conducted to study the evolution of the microstructure in crushed rock masses. Micro-CT system was used to observe the microstructure of the samples. Based on the average particle size,the particle crushing state of the saturated crushed limestone under compaction was obtained quantitatively,and the relationship between porosity and average particle size was analyzed. Using image tech- nology,the evolution of the particle shapes was studied quantitatively. The experimental results indicate that during compaction,particle crushing is pervasive,the pores in samples are compressed and filled with fine particles,and the connectivity between pores become worse. The initial gradation influences the porosity of samples. Under same axial stress,the porosity increases with an increase in Talbot exponent. The relationship between the porosity and the average particle size is linear,and the porosity can be used to describe the crushing state of the samples quantitatively. With the increase of axial stress,the circularity of the particles decreases monotonously,the shapes of the particles are more regular,the relationship between circularity and axial stress can be fitted by an exponential function. The study is help- ful for a better understanding of deformation mechanism of crushed rock mass.