Abstract: As a key consideration in drilling equipment, the bearing capacity of a derrick is closely related to the safety of the operating drilling system. To forecast the safe bearing capacity accurately, a method of stratified model updating which considers static and dynamic performance is proposed. Based on sensitivity analysis and engineering practice, an optimal updating function is established using the residual between test and theory parameters. Combined with a first-order optimization algorithm, an improved objective function is deduced to solve this problem. Simulation analysis is carried out for an in-service derrick on an offshore platform. The results indicate that the modified model can reflect the static and dynamic performances of the structure completely and accurately, thus certifying the feasibility and validity of this method. Then the modified model is used for dynamic simulation of the drilling loading condition, analysis of frequent seismic response, and double nonlinear analysis of unexpected extreme conditions. The failure shape, dangerous position, and ultimate bearing capacity can be predicted. It provides a new method for the prediction of safe bearing capacity and unexpected extreme condition of in-service derricks, which has practical value.