Effect of size on crushing strength of rockfill grains is studied using the particle flow code. Firstly

a discrete model of rockfill grains is developed using secondary development method with FISH language

in which particle shape and breakage behavior of rockfill grains are replicated reasonably. Then an equivalent simulation method is proposed to investigate the effect of size on crushing strength of rockfill grains in various particle sizes. A negative power formula is presented to describe the relationship between crushing strength of rockfill grains and its particle sizes. The meso bond strengths of contacts inside an aggregate model of rockfill grain are dependent on the size of the aggregate itself. Then

one dimensional compression tests of rockfill grains in lab are replicated based on the proposed numerical method to verify its accuracy and validity. At the end

influence of shape of rockfill grains on distribution of crushing strength is studied. Several basic conclusions are obtained: 1) Size effect on crushing strength of rockfill grains due to microcracks can be simu-lated equivalently by the way that meso strength of contact in the numerical model of rockfill grains decreases while the size of rockfill grains increases; 2) Crushing mechanical of rockfill grains is influenced by the particle shape

and square grains are usually crushed in compression-shear mode

while irregular and round grains fail in tension-shear or splitting mode. As a result

crushing strength of square grain is usually much higher than that of irregular and round grain; 3) When fail in tension-shear or splitting mode

dispersion of crushing strength of rockfill grains is dependent on shape of rockfill grains. The regular particle shape presents higher Weibull modulus

indicating smaller divergence for the crushing strengths. The breakage behavior of rockfill grains with different sizes under load pro-vides a reasonable method to predict the evolution of particle size distribution of rockfill assembly.