Abstract: Based on an urban rail transit subgrade widening project in eastern coastal soft soil area of China, a geotechnical centrifugal model test is conducted by using the L-30 geotechnical centrifuge of Tongji University, to study the horizontal deformation patterns of soil and pile in existing CFG (cement fly ash gravel) pile composite foundation subgrade under the action of adjacent loading. Then, the finite element numerical simulation method is used to study the influence of existing subgrade and new subgrade reinforcement forms on horizontal deformation law of the existing subgrade. The result shows that under the adjacent loading, the horizontal deformation of the soil pillars, which are located 2 meters away from the subgrade slope foot of urban rail transit line in soft soil area, demonstrates a pattern of bow-shaped deformation, the horizontal deformation increases first and then decreases during the continuous increase of burial depth. The CFG piles in CFG pile composite centrifuge subgrade demonstrate a funnel-shaped pattern deformation, the horizontal displacement is the biggest at the pile top, and decreases during the continuous increase of burial depth; the existence of pile foundation in the newly built line subgrade can effectively reduce the horizontal displacement amount of the existing subgrade, while adding a plank on top of the CFG pile can change the horizontal deformation pattern of the CFG piles from the funnel-shaped to the bow-shaped, the maximum horizontal deformation of the pile body can also be reduced.