Based on the joint probability density function of wind speed and wind direction (JPDF) and equivalent narrow-band analysis method, new formulation, in the continuous integration form, for evaluating wind-induced structural fatigue life has been derived in this paper. The formulation is proved to be consistent with its traditional counterpart which is expressed in discrete form. The calculation procedures for marginal distribution function of wind speed and wind direction, and the JPDF model are explained. The applicability of the proposed method is validated by estimation the fatigue life of a steel antenna. The JPDF is first determined using field measured wind data, the fatigue lives at some key points are then computed. The result demonstrates the applicability of the new formulation.