Red rock filling is widely used in construction projects in the southwestern region. It’s strength of the particles, permeability after compaction are closely related with crushing and the actual distribution of the particles.Based on compaction test of different gradation and different moisture contents of mudstone, the relationship among changes of particle size and the feature of particle breakage are studied .The results show that the increasing of moisture content and coarse particle is likely to conduce to exacerbating the crush of the mudstone. The sample’s gradation is more perfect after the compaction. What’s more, the water has little impact on the gradation and particle breakage when it approaches to 10 percent. When P₅ is invariant, the breakage increase with the increase of moisture content; when the moisture content is invariant, there is a direct proportion relationship between the increase of breakage and P₅.It’s better to use broken rate in evaluating the actual impact of the action of water, but as to other factors, there are certain limitations.