Abstract: The differences between the peak load and the operation task in the normal operating conditions of the nuclear power plants are compared from three aspects of operator training, task type and working load. Compared with the operation tasks under the normal working conditions, the mental load and the physical load of the operators would be changed greatly, which would lead to the difference between the operator's cognitive model and the human error mode compared with the conventional working condition. The existing HRA methods and models are difficult to satisfy the operator's reliability analysis, so a new HRA method is needed to solve the problem of the reliability under the background of continuous and fast changing of control tasks in the nuclear power plants.