The objective of this paper is to investigate the effects of initial particle gradation and rock content on the crushing behavior (i.e. grain size before and after crushing) of weathered phyllite fills. Compaction tests were conducted on weathered phyllite fills with rock contents of 35%, 45%, 55%, 65% and 75% (by weight). First, the particle size distributions (PSDs) were observed before and after compaction, and then the particle breakage of weathered phyllite fills was analyzed by fractal dimension. Relative fractal dimension was proposed to evaluate the effects of initial rock content and initial gradation on the particle breakage. It was found that the fractal dimension method can well characterize the crushing behaviors of the weathered phyllite fills. The finer the fills were, the more they were compacted. That is, after the first compaction, the relative fractal dimension of the weathered phyllite fills increased as the rock content increased, reaching the values of 0.013, 0.016, 0.024, 0.037 and 0.08, respectively. After the second compaction, these relative fractal dimension values, dominated by the initial particle gradation, became 0.059, 0.072, 0.052, 0.095 and 0.118, respectively. In conclusion, the weathered phyllite fills with 55% rock content exhibited the least breakage and were most suitable for filling the subgrade. Findings in this paper will provide significant guidance for the construction of weathered phyllite filling subgrade in future projects.