Abstract: The soil arching effect commonly exists in geotechnical engineering. The trapdoor tests are conducted using transparent soil to study the influences of fill density on the soil arching effect. The results show that under the lower compactness of the fill, the smaller relative displacement can reach the steady stage of soil arching, and improving the compactness of the fill can reinforce the soil arching effect. The fill density has no influences on the height of the inner arch, but significant influences on the outer arch. When the relative displacement is between 0% and 3%, the displacement reflectivity increases rapidly, and then gradually reaches a constant. Improving the fill density is beneficial to weakening the reflection of differential settlement. This study may provide a references for the influence of fill density on the evolution of soil arching.