Abstract: Using the new shoulder balance weight retaining wall of an old embankment widening project of a mountainous highway as the prototype, four groups of geotechnical centrifuge model tests on displacement control are designed. The influences of compactness and reinforced fill on the earth pressure on the wall and the deformation of the subgrade fill are discussed. The results show that: (1) the reinforced effect of backfill to reduce the earth pressure increases with the increasing degree of compaction. When the compactness is smaller than 95%, the reducing area of the earth pressure is mainly located in the lower half of the upper wall; (2) the equilibrator has uplift effect on its overlying soils so as to reduce the earth pressure on the lower wall, and the influence area below the equilibrator is about 1/3 height of the lower wall; (3) the reinforced soils can improve the resistance to the deformation of subgrade fill and thus reduce the settlement of surface fill caused by the lateral displacement of wall, and the uneven settlement between the old and the new subgrade is significantly mitigated.