In order to meet the requirements of users as much as possible in case of being lack of power supply， an approach to obtain the optimal peak load shifting plan is proposed. The management of working schedule regulation and holiday staggering plan are regarded as genes. The summation of products between affected user number and affected time or the summation of products between affected kWh and affected time are used as the index. The genetic algorithm（GA） is introduced to get the best peak load shifting plan in a certain operation mode. A single-step process on loop switches is defined to adjust the operation mode. A heuristic method is developed to obtain the optimal plan in all operation modes. By using random initial value process， the possibility to reach the global optimum solution is remarkably increased. A typical three-section-three-connecting grid is given as an example to show the feasibility of the proposed method. It is also shown that the property of the result improves with the increasing of the number of involved elements.