How to predict the partially penetrated settlement of soft soil under plastic drain plate is a difficult problem in the design of large area thick soft soil foundation treatment process. Based on the foundation treatment process of the Yushan reclamation project，we combine with observation data of settlement from the beginning of construction to the end of construction，analyze the settlement and settlement history of typical areas，compare the final settlement calculated by the measured settlement data with that calculated by the theory，and analyze the reinforcement effect of deep plastic drainage plate. The results show that the drainage efficiency of the plastic drain plate below a certain depth rapidly attenuates，resulting in the consolidation rate falling behind the theoretical calculation rate. The settlement under the plate should be corrected when the final settlement is calculated by the hyperbolic method combined with the measured data.