The recent development and commercialization of offshore wind turbines has led to a significant increase in capacity, reaching 15 MW. This has inevitably resulted in a corresponding increase in the size of the blades and towers, along with the nacelle weight. Although the cylindrical tower has a simple structural shape, it is a critical component that must be sufficiently secure to support the thrust and moments generated by the blades as they rotate, the nacelle and blade gravity, and the wind loads experienced by the tower itself. Compared to other factors, the risk of loss in case of damage is very high and accounts for 25% of the wind turbine price. The main target of this research is wind turbine towers, and we propose a simplified methodology that allows for a more intuitive validation of structural safety assessment under complex time-history load combinations. The program used for the structural safety evaluation was NASTRAN, and the applied load was calculated by applying the in-plane shear load information from the wind turbine analysis. In order to review structural safety in a short period of time, complex load combinations were simplified, and extreme loads, buckling, and fatigue life were examined sequentially. The minimum life point of the weld according to the finite element analysis method was 112.5 years when calculated using EUROCODE 3. This code considered variable fatigue loads differently. Moreover, as the code considered experience factors, a direct comparison with other methods was not possible; however, a similar trend was observed. The combination of the proof-loading methods presented in this study facilitates the verification of the structural safety of wind turbine towers in a short duration, thereby increasing confidence in the final weight.