Abstract: The geotechnical properties of deep-sea soft clay are quite different from those of terrestrial or offshore clay. For the representative deep-sea soft clay collected from the western region of South China Sea, an improved full-flow penetration device is used to measure its strength characteristics. Combined with (Focusing on) the special micro-structure and bio-silica minerals, the cyclic degradation characteristics are analyzed and discussed. The results show that the deep-sea soft clay in the western region of South China Sea generally has the characteristics of high water content, high liquidity index, high activity, low undrained shear strength and high sensitivity. The extremely slow deposition rate and stable deposition environment are the main reasons for the high sensitivity of deep-sea soft clay. The change of micro-structure of soils during the full-flow cyclic degradation process is mainly caused by the damage of flocculation and the change of pore structure. The bio-silica particles may break under the cyclic penetration, leading to the release of the internal pore water, which will aggravate the degree of degradation.