Abstract: Taking long-distance large-scale wind farms connected to the grid as the research background, and considering the synchronization effect of environmental factors on the current-carrying law of the transmission line and its mechanical performance degradation, electro-thermal coordination theory and line aging failure model are organically combined. Based on the electrothermal coupling and life-cycle cost, the maximum allowable temperature assessment model for renewable transmission lines is proposed, which provides an evaluation basis for the renewable energy consumption capacity and operation performance of the grid.The model continuously processes the environmental variable values according to various setting schemes of maximum allowable temperature, and simulates annual variations of electrical and physical state parameters of the line based on the thermal inertia equation of the overhead conductor.Then, the duration of each temperature interval is calculated and the life-cycle performance of line is predicted based on the aging failure model of transmission line. The life-cycle cost of the line can be obtained according to the failure rate model, the annual average profit of investment for transmission line and analytic function expression of the maximum allowable temperature for transmission line on the premise that the access income of unit wind power is fixed, thereby achieving the goal of maximizing the annual average profit. Finally, effectiveness of the proposed model and its effect on improving the economic and safety of the system operation are verified by the actual case study.