When large-power disturbances occur in power grids, the system frequency will shift greatly, and there may be obvious spatial-temporal distribution characteristics. By analyzing the single-machine frequency response characteristics of the system and the frequency difference between the two systems, a system frequency analysis model considering nonlinear factors under large frequency difference is proposed to estimate the maximum offset of the system frequency. It is proposed to reduce the maximum frequency offset and improve the frequency spatiotemporal distribution characteristics by selecting the coordination method of emergency control at different locations at different times, thus enhancing the safety and stability of the power grid. This work is supported by the Science and Technology Project of State Grid Corporation of China (No. 4000-201940418A-0-0-00).