Intelligent transmission line construction is the concrete practice of deep integration of a strong smart grid and ubiquitous electric power internet of things, with five basic characteristics, i.e. essential security, real-time perception, holographic interconnection, autonomous early warning, and intelligent disposal. Realizing intelligent dynamic capacity increase of the thermal stability of transmission lines based on intelligent transmission lines is undoubtedly one of the most applicable scientific methods to improve line transmission capacity in the future. The intelligent capacity increase decision system based on a smart transmission line is integrated into the overall scheme of smart transmission line construction. Relying on domestic mainstream EMS, it controls transmission network operation data and meteorological conditions in real time through an acquisition support device. Then it is transmitted through the convergence link to the monitoring master station and the thermal stability transmission capacity calculation system. The intelligent calculation and analysis of the thermal stability transportation capacity with the line as the unit is realized in the basic application layer. Furthermore, the innovative proposal of realizing expert auxiliary analysis and decision-making for intelligent capacity increase in the professional application layer will push the final auxiliary decision-making related strategies to the operational and control personnel automatically, intelligently and in a friendly fashion. This realizes the intelligent, fast and effective control of the heat stable transmission capacity of the line and significantly improves the intelligence and practicability of dynamic capacity increase technology. The example analysis shows that the method is scientific, practical and applicable, and could be applied to other provinces and cities. This work is supported by the Science and Technology Project of the Headquarters State Grid Corporation of China (No. 5108-202040024A- 0-0-00) and the Science and Technology Project of Water Resources Department of Zhejiang Province (No. RC2016).