<p>The development of offshore wind turbines is driving advancements in jacket structure–foundation design. This study presents a fatigue reliability analysis for spacial KK-type cast steel nodes used in the jacket structure of a 16 MW offshore wind turbine. It integrates the combined effects of marine environmental loads and wind turbine–induced dynamic loads. Reliability assessments are conducted for both the cast steel part and its weld joints. Stress amplitudes at critical locations of the cast steel component are determined via finite element modeling, and the weld fatigue life is evaluated using the hot spot stress method. To account for the variability in wave loads, a novel reliability analysis method is developed, utilizing a joint probability density function of wave height and spectral peak period, complemented by large-sample sampling, addressing limitations for fatigue-life prediction in existing datasets of joint wave statistics. The fatigue reliability of the cast steel part is calculated to be 1, while the reliability of the associated weld segments is determined to be 99.94%. This study highlights the improved fatigue performance of cast steel nodes and provides a practical approach to reliability analysis under “complex marine load” conditions, offering innovative insights into offshore wind turbine design.</p>