An online calculation method for stability section power limit based on real-time microclimate environment and operation mode is proposed. Static stability section limit is transferred to dynamic limit which changes with real-time data, offering technical support to lean regulation of power grid. Based on dynamic capacity-increasing technology, microclimate data in external system is accessed to regulating system and dynamic current carrying capacity of transmission line is calculated. Based on power grid model and real-time operation mode, branch open distribution factor is adopted to calculate dynamic power flow transfer ratio of transmission sections. Based on power transfer distribution factor of node-branch, the influence of stability control device action to transmission section power is analyzed real-timely. And section power limit is modified dynamically. The method has been used in Nanjing district regulating system online. Actual running data is used to verify the results, proving the efficiency of algorithm to improve the transmission capacity of sections in peak period. This work is supported by Science and Technology Project of State Grid Corporation of Cina “Research on Key Techniques of Transmitting Capacity Promotion of Urban Core Transmission Line.”