Crushed rocks, especially mudstones, whose seepage properties are strongly influenced by particle mixture during compaction due to muds will be washed away after water flow. The present study focuses on the porosity evolution, particle crushing and non-Darcy seepage properties, during the compaction, of a crushed mudstone particle size mixture. An experiment based on a self-designed water flow apparatus, the MTS 815.02 system and a non-Darcy testing method were performed to investigate the effect of particle size mixture on seepage properties and compaction behavior of crushed mudstones. In particular, the Reynolds number calculation of particle mixture shows that water flow has involved the influence of non-Darcy flow. Testing results indicate that: (1) The porosity of crushed mudstones is strongly influenced by compaction (axial displacement) and particle mixture. The porosity decreases with the increase in axial displacement and decrease in bigger particle size, respectively. (2) During the compaction, some larger particles were crushed which is a main reason to cause size 0-2.5 mm. Muds washed away are the main reason for weight lost in mudstone samples due to the effect of water seepage. (3) Non-Darcy seepage properties of crushed mudstones were strongly influenced by mixture sizes and compaction, and in general, during the axial compression, the permeability decreases while the non-Darcy coefficient increases with the decrease in porosity . (4) The fluctuations of - and - curves show that the lager the particle size, the more the fluctuation displayed in the curves. The permeability of minimum size shows one order of magnitude less than that for largest one. (5) The porosity, particle crushing and seepage properties of crushed mudstones are not only related to compaction levels, mixture sizes, but also related to the style of arrangement.