As a new type of structure,the application of insertable large-diameter steel cylinders in China is still in its infancy,and there is an urgent need to conduct in-depth research on the applicability and stability of large-diameter steel cylinder foundations under super-thick soft soil foundations.We carry out the stability research of steel cylindrical structures under different water depth conditions,different penetration depths and different geological conditions by numerical simulation calculation methods.The results show that when the depth of the rotation center is less than the burial depth,the mechanical mechanism of the large-diameter steel cylinder is mainly manifested as rotational overturning,which is a deep-insertion structure.When the depth of the rotation center is greater than the burial depth,the mechanical mechanism of the large-diameter steel cylinder includes rotational overturning and horizontal sliding,which is a shallow-insertion structure.The failure mode of steel cylinders is related to dimensions,burial depth,load magnitude,and soil parameters,etc.Under the condition of super-thick soft soil geology,the steel cylinder structure can still be applied.When the S/H (S is the horizontal displacement of the top of steel cylinder,and H is the height of the cylinder body above the mud surface) of the steel cylinder is 1.5%,the load value increases with the increase of the insertion ratio,the cohesion of the soil,the internal friction angle of the soil,and the backfill depth,and decreases with the increase of the load height.