For the large-scale synchronous AC grid，the large disturbance within the region will impact not only the grid stability in the region，but also that in other regions through the interregional tie-line，even leading to interregional tie-line power oscillation split.Following a look into the large disturbance impact characteristics on the tie-line between regional power grids，the disturbance impact start time and impact time are defined based on the characteristic of tie-line transient potential energy to quantitatively describe the disturbance impact process of the large fault.According to the relationship between tie-line potential energy and the active power at disturbance impact time，a tie-line stability criterion is also proposed，thereby forming a quantitative description method of the large disturbance impact characteristics based on the energy function.The method proposed is verified in the Central-North China power grid.