Due to the topographic limitation in the mountainous area, the traffic forms such as high fill slope and bridge are not uncommon, and the limitation of the terrain leads to the difficulty of transporting the prefabricated components of the bridge structure, and the prefabricated beam yard can be arranged on the high fill roadbed to solve the problems of mountainous terrain restriction and the transportation difficulty of the prefabricated components of the bridge. Therefore, in order to solve the problem of the layout of the sunken precast beam field of the high-fill subgrade, this paper analyzes the main factors of the settlement and deformation of the fill subgrade, applies a variety of deformation control measures to control the deformation of the high-fill subgrade and the precast beam field, and analyzes the deformation characteristics of the fill subgrade and the beam field through a three-dimensional numerical model. The results show that the uneven settlement of the precast beam field can be effectively reduced by replacing the lower layer of soil with poor physical properties and using the filler layer with better physical properties. After the settlement control measures were adopted, the overall settlement of the precast beam yard was 20 mm, but the uneven settlement was only 3 mm. The influence range of the precast beam yard on the lower filler during the construction period is similar to that of the beam yard area.