Abstract: The present disclosure relates to a method and system for fatigue analysis on an offshore deepwater drilling conductor or surface casing. The method includes: obtaining a dynamic soil reaction curve of soil where a conductor or a surface casing is mounted, with consideration of a cyclic decline effect; obtaining a stress response time-history of a hot spot position of the conductor or the surface casing under a dynamic load in each direction, thereby forming a first stress response time-history; obtaining a stress response time-history of the hot spot position of the conductor or the surface casing coupled with a soil reaction under the dynamic load in each direction in combination with the dynamic soil reaction curve and the first stress response time-history, thereby forming a second stress response time-history; and performing fatigue life prediction on the surface casing or the conductor by using the second stress response time-history.