Abstract: Particle breakage is a key factor that influences rock-fill strength and deformation.However,particle breakage laws of rock-fill material are still unclear and the breakage standard of the rock-fill particles is also absent. Single-particle compression test is a key method to study the breakage characteristics of rock-fill particles.In this test, 920 groups of visual-single-particle compression experiments were performed, by which the failure process of different size particles were investigated.It is noted that the destruction process of particles can be divided into four stages and the failure modes can be divided into three types. Moreover, the damage of broken particle increased with the decrease of particle size.The single-particle strength parameters of the same size could be accurately simulated by the Weibull model.As the samples increase, the distribution of peak strength gradually tends to be the normal distribution.?Furthermore,gradation distribution of the broken particles is related to the failure?mode. Particle gradation of the broken particles, which reveals several peak strengths, conforms to fractal distribution.