The deep soft soil layer of the 4th runway at Pudong Airport was studied in this paper. During preloading test，the ground settlement deformation law was analyzed and compared under two conditions，using plastic drain plate or without. It was found that during preloading，both the ground settlement and settlement rate in areas using plastic drain plate were much larger than those areas without plastic drain plate. The instantaneous settlement during preloading was both large in two conditions，which both exceeded 50% of the total settlement during whole preloading process. During the process of surcharge preloading，compared to actual loading，the state of the ground soil would appear that shallow soil was over consolidation while the deep soil was still under consolidation. Therefore，for deep multi-layer soft soil ground，residual settlement should be calculated layered and separately after unloading. The research results would have important reference significance to the design and construction of soft soil foundation treatment project.