The constraint conditions of filler on construction plane of embankment filling vary remarkably for each part. In particular, the compaction of soft-rock filler with low particle strength and weak structural lock effect is higher close to the center than that close to both sides. We carried out experimental study on an embankment project with sandy mudstone filler, and the results manifested that: 1) the measured compaction degrees of filler close to the center and both sides are not lower than 0.95 and 0.93, respectively, which meets the compaction requirements of embankment for second class highway, yet still with some difference; 2) large-scale triaxial consolidated-drained test was conducted on the rolled filler collected on site at the compaction degree of 0.95 and 0.93, respectively, and the results revealed stable cohesion and larger friction angle of sample at 0.95 compaction degree than that at 0.93 compaction degree by 13%; 3) in large strain process, the volumetric strain was generally irrelevant with confine pressure at the compaction degree of 0.93, dominated by mesostructure compression, while at the compaction degree of 0.95, volumetric shrinkage was positively correlated with confining pressure despite more sufficient stress in particle skeleton, implying that the large strain process was accompanied by secondary compaction after particles breakage; 4) at both compaction degrees, the relations of spheric stress versus volumetric strain and volumetric modulus versus confining pressure both obey linear fitting relation. Duncan-Chang E-B model could well describe the deformation mechanical characteristics of soft rock filler under different compaction degrees.