To increase the energy density in order to meet the demand of electricity use, wind turbines have been developed toward large-scale designs. The gigantic size of wind turbine towers can generate more electricity, but it will also create higher cost of development and maintenance, and impact the operation life. The present research sets up a wind turbine tower model, and the loads of towers are calculated by its relation to wind speed. Finite element method is used to analyze the stress distribution of towers under the loads. Impacts from different loads are compared as well. The wind speed distribution is derived from data collected in Penghu, Taiwan using statistical method. Fatigue analysis of towers is then conducted with fatigue loads and wind speed distribution, and the mean time to failure (MTTF) of towers is calculated with quantitative reliability theory. The result shows that the main loads of towers are the wind force acting on the rotation area of wind turbine blades and the moment caused by non-uniformed wind speed. After comparing this research results with loads calculated by a wind turbine design software, it is concluded that it’s a feasible and conservative method to analyze wind turbine tower structure with the loads calculated by its relation to wind speed. In addition, it is shown that the average and maximum hourly wind speed in Penghu can both be fitted into Weibull distribution. In conclusion, the fatigue analysis shows that the probability is greater than 99.8% for the tower model’s failure time to be above 331,416 cycles, and it shows that the tower model in this research possesses appropriate fatigue durability and is considered a safe tower design for Penghu.