The under-frequency load shedding ( UFLS) is considered as the last effective remedial measure against a severe frequency decline of a power system.Aiming at this issue,an optimal UFLS strategy considering distributed generator ( DGs) and load static characteristics is proposed based on the frequency and its change rate. This strategy consists of several basic rounds and a special round. In the basic rounds,the system emergency can be alleviated by quickly shedding some loads runs by runs according to the feedback control law. In the special round,by optimizing the output power of DGs and adjusting some loads,the system security can be regained and the corresponding ope-rating parameters can be optimized. Finally,the effectiveness of the proposed optimal UFLS strategy is verified with the modified IEEE 37-node test feeder as an example.