In order to solve the problem of overly complex calculation of time-domain fatigue analysis, a method for evaluating the cumulative fatigue damage and reliability of structural fatigue based on frequency-domain excitation spectral analysis considering average stress and non-Gaussian correction is proposed. This method is suitable for metal structures whose working state can be approximated as linear elastic and dominated by high-cycle fatigue, under the action of random pulsating wind or similar narrowband and broadband excitation. A certain offshore wind turbines tower is taken as an engineering example to calculate the fatigue damage value in the area of maximum stress of the tower, while to compare and analyze the time-domain reference solution with the Rayleigh frequency-domain solution. The results show that the deviation between the Dirlik frequency domain solution and the reference solution is 7.80%, and the Rayleigh frequency-domain solution is as high as 17.65%, and the proposed method has more advantages in terms of calculation accuracy. The results of the reliability analysis indicate that the failure probability of the wind turbines tower after 20 years of service is 37.19%. Based on this, the tower can be reasonably replaced or repaired in accordance with relevant regulatory requirements. The research results can provide a reference for the assessment of cumulative fatigue damage and reliability of engineering structures.