Abstract: The Spar platform has become more and more attractive as its superior motion and stability properties in deep-water oil exploration industry. Upending of Spar is a critical process because the motion and structural loading applied is substantially different from the exploratory life, so it needs special design and verification. An analysis method of upending process is presented based on the fundamental principle of vector form intrinsic finite element (VFIFE). In this method, the effects of gravity, damping force, hydrostatic pressure and additional water mass are considered, and the coupling relationship of load, motion and mass is built. It can simulate the upending and provide information on structure motion during the process. The import method of motion information is built by inputting the motion characteristics into the analysis software ANSYS, and then performing detailed strength analysis. This method has the ability to make an elaborate analysis on both the strength behavior and the motion response of structures in time-domain. An actual upending analysis of Spar is utilized for demonstrating the feasibility and highlight of the method.