With the wide application of the phasor measuring unit（PMU）/wide area measurement system（WAMS），the security and stability technology based on actual response has become a research hotspot.This paper first analyzes the relationship between the voltage at the oscillation center and the transient stability of the power system，and then presents a real-time detection method for transient instability based on the perturbed voltage trajectories.According to the voltage trajectories after perturbation，compound integration calculation is carried out.The voltage at the oscillation center of the system mapping the relative movement information of generator groups is used to quantitatively assess the transient stability of the whole network.Different from the detection methods based on power angle trajectories，the proposed method can be applied to multi-swing stability analysis characterized by small calculation amount，good fault tolerance and without quick division of the generators into groups and the inertia computing center of the system.