Abstract: The analysis of static stability is an important process in the design of semi-submersible, the complexity of the geometry of semi-submersible poses difficulties for analysis of static stability. This paper describes the surface modeling technology, focus from geometry to the surfaces; in consideration of the floating platform complex geometry, proposes radiate integral, used to calculate the area of waterline, centroid of waterline, drainage volume, floating heart; A coordinate transformation algorithm based on vector projection is proposed, calculation of buoyancy parameters for tilting and draught of offshore platforms. Based on the calculation of the basic parameters of buoyancy and the transformation of coordinate system, Calculation of static stability can be calculated.