The dynamic capacity increase of overhead power transmission lines is important to enhance the efficiency of power systems, especially under high wind conditions. This study proposed a method to calculate the maximum allowable ampacity of the transmission line considering the limitations imposed by line sag and temperature. By integrating the calculation of conductor sag under wind conditions with the state equation of the conductor, the maximum horizontal displacement of the conductor has been calculated. This parameter is then used to ascertain the maximum allowable operating temperature, which is subsequently applied to the load flow calculation model to determine the maximum allowable current. The results show that when the wind speed exceeds 18.2 m/s, the maximum allowable operating temperature and ampacity of the transmission line decreases rapidly. The proposed method aims to provide a practical approach for transmission line operators to dynamically adjust the load carrying capacity of transmission lines under varying environmental conditions.