Abstract: As a high-voltage transmission tower-line coupled system is sensitive to wind, the wind load is an important control load in both its design and actual working condition. The joint probability density function in the wind direction and speed are very important in both structural engineering and wind energy, but it is much difficult to model a joint distribution considering both wind speed and wind direction simultaneously because of the correlation between wind direction and speed. Based on multiplication rules in probability theory, a mixture distribution model is first derived by taking daily extreme wind speed records in Chongqing city as an object. And the deficiency of mono-probability distribution is remedied by the mixture distribution model. Meanwhile, according to the recorded data of different wind directions, the probability density model in the wind direction is proposed, and the joint distribution model for both wind direction and speed is obtained by multiplying the distribution model of wind speed and direction together. Then the method for calculating the wind-induced fatigue of a transmission tower-line coupled system is proposed by combining with the joint distribution model and the Miner law. At last, the wind-induced fatigue of an ultra-high voltage transmission tower-line coupled system is also studied by the proposed method, the effect of wind speed and direction on the wind-induced fatigue of a transmission tower is exactly considered, the calculation is decreased effectively and the efficiency is also improved significantly.