Abstract: The natural ground of a object can not meet the requirements of bearing capacity and differential settlement and there is thick filling which is based on fly ash under the foundation, so the natural ground need to be reinforced. Firstly, comparing the two different treatment schemes and considering the fly ash is good building material, the final scheme is that adopting the cement deep mixed piles to reinforce the filling layer to improve the bearing capacity of the natural ground, and using CFG piles to handle the deep soil to meet the requirement of settlement. Secondly, according the final scheme, using the finite element software PLAXIS 3D to build two models to compare and analyze the settlement, model 1:composite layer model, model 2:pile unit model. The final simulation results were compared respectively with the measurement data of settlement, and the comparison can provide some guiding significance for the future engineering.