Abstract: BOC has accumulated a great deal information of seafloor soil and pratical penetration depth of leg footing of jack-up for many years. On the basis of analysing these informations and Comparing investigative data with the results of the theoretical calculation, the calculation methods of penetration depth into various seafloor soils were described systematically. And calculation formulae for the Bohai seafloor soil and selection of the types of jack-up applicable for the operation in Bohai were proposed in this paper.