The method of practical fatigue strength analysis for the hot-spot parts around leg nodes of the Jack-up rigs is seemed to be behind the demand because of their unique operating systems and complicated mechanism of axial force occurrence in braces. In order to estimate the fatigue strength at leg nodes, the forced vibration analysis for irregular waves in short and long-term sea conditions is mandatory. In this paper, the method of the forced vibration analysis in the regular wave is developed for the irregular waves and the method to estimate the long-term distributions of axial force amplitude in braces is introduced by applying the simple formula in the previous paper. For the estimation, the probability of occurrence of wave incident angle, operating sea depths and whether the wedges are installed or not are considered. The fatigue strength at nodes can be estimated by the combinations of long-term distribution of hot-spot stress amplitudes calculated from axial force in braces and the S-N curve for the used material.