The reverse distribution characteristics of energy distribution and load demand have contributed to the formation of multiple large-scale power and energy transmission systems in China. Under unexpected large disturbances, a first pendulum instability of the system will occur and the adaptive reclosure finds it difficult to improve system stability. Therefore an additional stability control strategy for adaptive reclosure under emergency power support is proposed. First, the scenario of system first pendulum instability and the instability conditions are analyzed, and the prediction method of the first pendulum stability based on the ultra-real-time prediction of power angle is established, and the optimal prediction order required for a long period is demonstrated. Further, combined with the DC channel to provide emergency power support to absorb the unbalanced energy of the system, the adaptive reclosure additional stability control strategies based on advanced pre-control are given. From the results of instability judgment, the predictive control timing is elucidated. The emergency power support based on optimal reclosure time reduces the power angle pendulum of the system to the greatest extent. This solves the problem of the lack of a reclosure scheme when the first pendulum of the transient fault is unstable. Finally, a large-scale power transmission model is established based on PSCAD/EMTDC, and the effectiveness of the proposed adaptive reclosure additional stability control strategy is verified by simulation.