The rule No.599 of power grids in China indicates that the shedding load is equivalent to the failure loss load, which requires less load-shedding as much as possible under the premise of security and stability, to reduce the cost of frequency accident control. Therefore, in this paper, the load-shedding contribution factor based on frequency regulation effect, P-V characteristic and the importance of the load is designed to indicate the placement of load shedding and the allocation of the load to be cut. The influence of voltage leap on unbalanced power is analyzed to improve the calculation accuracy. A dynamic correction scheme is described to adjust load-shedding amount of each steps according to change rate of frequency derivative, to fully utilize the self-recovery capacity of system frequency. Simulation based on IEEE 39-bus system shows that the new strategy could reduce the load shedding amount and improve frequency recovery process, in which both the reliability and economy are taken into consideration.