Research purposes: Alluvial mid － compressible clay on fluvial high terrace is widely distributed at the Being －Shanghai high speed railway，which has a characteristic of high natural strength． Generally，there is no stability problem of filling and it can meet the need of engineering with no strict requirement for settlement when it at natural condition or after shalow layer treatment． However，ballastless track in high speed railway has strict requirements for subgrade residual settlement; Furthermore，current theoretical methods for calculating total and residual settlement of this type of soil can not meet the design requirement． So，through analysis of the basic characteristics of foundation soil and in － suit filling experiment on natural ground of Beijing － Shanghai high － speed railway，the settlement analysis method of this type of soil is studied．
Research conclusions: Basic characteristics，especially strong structural characteristic and high yield strength characteristic of mid － compressible clay on fluvial high terrace are summarized in this paper． Deformation law of this kind of foundation soil under low loading level is analyzed; At last，different calculation methods are proposed to calculate different settlement，that is，elastic theory method and proportion of settlement － completion method based on elastic method can be used in total settlement and residual settlement calculation respectively． Generally speaking，after the load stable for 6 months，completion of the settlement ratio can be up to 90%．
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