In a nuclear power plant, small branch piping has an external diameter of less than or equal to 60.3 mm, widely distributed in multiple systems. The piping is welded connection to the main piping, e.g. socket or butt welding, through variable diameter fittings. In the weld joint area, fatigue failure usually occurs, due to stress concentration. The experience feedback of operating plants indicates that, the fatigue failure of small branch piping accounts for the majority of piping fatigue failure, resulting in a piping leak or break, etc. Even further it leads to power reduction, reactor or turbine shutdown. At present, the nuclear power plant critical component management is used for the risk classification purpose, to identify the equipment that will lead to a reactor or turbine shutdown. However, the management does not include small branch piping. Therefore, the paper proposes a risk classification method for nuclear power small branch piping. The method includes three important parts, i.e. the identification criteria of failure consequences, the evaluation model for failure probability, and the preventive maintenance strategy that consequences and probabilities are taken into account comprehensively. The paper is structured as follows: Firstly, some typical cases of small branch piping failure are introduced in detail. And then, the reasons, processes, and consequences of cases are analyzed. Subsequently, the risk classification method of nuclear power small branch piping is introduced. At last, an application example is illustrated to show how it works and some efforts that can be conducted for preventive maintenance.