The invention provides an online safety and stability trend analysis method for a large power network. The method comprises the following steps: I, online safety and stability analysis is carried out according to the current operating mode of the power network, and the safety and stability estimation result of the power network at the current operating network is generated; II, the estimated future operating mode of the power network is adjusted according to the current operating mode, the ultra short-term load forecast, an ultra short-term new energy source forecast, real-time power generation plan and scheduling operation of the power network; III, the online safety and stability analysis is carried out aiming at the future operating mode of the power network, and the safety and stability estimation result of the power network at the future operating state is generated; IV, the safety and stability estimation result at the current operating state and the safety and stability estimation result at the future operating state of the power network are determined; V, the safety and stability trend level of the power network is determined; VI, the evolution trend of the power network in the future is estimated according to the result of the level. The method provided by the invention can carry out safety analysis on the power network in advance, stability problems and development trend of a power system can be pre-estimated, so that the early warning of accidents at future states is realized, and corresponding early warning and decision information are provided.