Abstract: Secondary consolidation deformation and structure of soil are produced during naturally sedimentary process due to time effect, and then the consolidation yield stress increases. Bjerrum model is not proper for the deformation mechanism of secondary consolidation of structural clays. Based on oedometer tests on Lianyungang structural clays and the concept of void index proposed by Burland, the deformation mechanism of secondary consolidation of structural clays is studied. Change of void ratio index (?Iv) ranges between the intrinsic compression line (ICL) and the compression line of natural sedimentary structural clays. When the consolidation pressure is less than the yield stress (termed as preyield state), the structural strength provides the resistance to the compression potential of void. As a result, ?Iv increases with the consolidation pressure before yielding of soil structure and the secondary consolidation deformation can be ignored during this stage. When the consolidation pressure exceeds the yield stress, ?Iv decreases with the increase of the consolidation pressure mainly due to the collapse of the large void structure. The coefficient of secondary consolidation, Cα, reaches a peak value at the critical yield state and then decreases with the consolidation pressure. It is concluded that the secondary consolidation deformation will not develop infinitely due to the existence of the compression line (SCL) of natural sedimentary clays.