In order to accurately estimate the fatigue life at tubular crossing nodes, a fatigue damage assessment was conducted on a specific offshore substation utilizing the time-domain analysis method. A local model for critical nodes of the foundation was established employing ABAQUS. The welds at each pipe node were selected as hotspots, considering the combined loads of wind, waves, and currents. Utilizing the rain-flow counting method in conjunction with the Palmgren-Miner criterion and S-N curve, a precise fatigue life analysis was performed on the key nodes of the structure. A comparative analysis was carried out using SACS, to validate the reliability of the local model. Results show that the fatigue strength of the substation meets the regulatory requirements within the design lifespan. The construction of the refined local model provides an accurate estimation of the fatigue life at tubular crossing nodes. Random waves 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.