According to the development program of UHV power grid， an inter-area synchronized power grid interconnecting North China power grid， Central China power grid and East China power grid. there is a new demand for the unified coordinative load shedding program and tie-lines separation of low-frequency settings. Modification suggestions are made for DL 428—91 《technical requirements for power system under-frequency load shedding》 . The effects of governor models and large-scale wind power on the scheme are analyzed. Theoretical analyses show that the adaptive load shedding method should not be large-scale used by theory. A HVDC modulation method is proposed to improve the system frequency stability under serious system faults， the simulation results demonstrate that the proposed method works well and reduces the risk of low frequency load-shedding in the power system.