In order to accurately estimate the fatigue life at tubular crossing nodes of the jacket foundation, a fatigue damage assessment is conducted on an offshore substation utilizing the time-domain analysis method. A local fine model for the critical nodes of the jacket foundation is established by Abaqus software. The welds at each node are selected as the hotspots, considering the combined loads of wind, wave and current. Through the rain-flow counting method in conjunction with the Palmgren-Miner criterion and S-N curve, a precise fatigue life analysis is performed on the key nodes of the structure. A comparative analysis is carried out using SACS to validate the reliability of the local fine model. The results show that: the fatigue strength of the substation meets the regulatory requirements within the design lifespan; the construction of the local fine model provides an accurate estimation of the fatigue life at tubular crossing nodes; the random waves can more effectively depict actual sea conditions, reflecting the stochastic and stationary nature of wave processes. The analysis outcomes will provide reference for subsequent research and practical engineering.