Research conclusions: (1)The numerical simulation and in situ observed data are used to compare and analyze the subsidence law of composite subgrade and it can be seen that the compression of soil between piles appears in 1／4—1／6 ranges of the pile bottom and the entry volume of pile end is up to 20％一30％of the total subsidence volume．(2)It can be seen from the subsidence—depth distribution curve that the compression depth of the soil body under the pile end is one tine of plane distribution width of pile．(3)The max．subsidence volume and construction—post subsidence calculated with finite element method ale very close to the observed data and the difference of construction—post Subsidence predicted with finite element method is smaller than that with experience formula．So the finite element method is worth using widely in calculation of subsidence．