In order to indentify the variation characteristics of the coefficient of secondary consolidation of soft clay at the estuary of the Pearl river delta, and provide a basis on the precise parameters of the settlement design for ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? the tunnel project of? Hong Kong-Zhuhai-Macao Bridge island? , we carry out a classification test and consolidation test on the undisturbed samples of grade I, so as to obtain the relative physical and settlement parameters, analyze the characteristics of the coefficient of secondary consolidation with load changes, and study the correlation between the coefficient of secondary consolidation, preconsolidation pressure, compression index , water content and plasticity index. The results show that the coefficient of secondary consolidation increases linearly with the increase of water content, plasticity index; the ratio of the coefficient of secondary consolidation and compression index is not a constant in the normal consolidation; the coefficient of secondary consolidation is small and increases with the load growth before loading is less than the preconsolidation pressure, it is from large to small with the load growth after loading is more than the preconsolidation pressure. This research ascertains the variation characteristics of the coefficient of secondary consolidation, founds the correlation of coefficient of secondary consolidation and related physical and mechanical indexes, and forms a regional guidance for the deformation calculation of soft clay at Pearl River Delta.