Along with the steady increase in power load of the regional power network， it often happens that the power grid runs beyond its schedule or the power device works beyond its safety restriction. The traditional method is to define a staggered peak load plan in advance， according to which the relatively unimportant load will have to be shed. However， this method cannot satisfy the real-time demand. An automatic load controlling system is designed according to the actual situation of Foshan power grid， while giving its design method and classification. The field running results show that this method can meet the real-time demand and supply power to users as much as possible on the basis of power grid safety.