Environmental qualification (EQ) is a process to ensure that equipment will be capable of withstanding the ambient conditions and executing specific function that the equipment is actually called upon to be performed under accident conditions. The main purpose of EQ is to provide reasonable evidence to ensure that common cause failures will not occur. Electric penetration assemblies (EPAs) belong to EQ components and perform safety-related functions. The time limited aging analysis (TLAA) of EQ components includes all long-lived, passive and active electrical components and commodities located in a harsh environment that are important to safety. This paper takes the electric penetration assembly (EPA) of a early domestic M310 NPP as the research object, based on the components, materials, environment, aging mechanisms and effects of EPA, combined with domestic and foreign standards, specifications and latest research results of equipment qualification and operation license extension, the time limited aging analysis key method of EPA of a early domestic M310 NPP is studied, the test scheme is designed, the test sample is selected, the key parameters are determined, the supplementary environmental qualification of EPA of a early domestic M310 NPP is finished. At the same time, combined with the current management status of EQ equipment at home and abroad, some management suggestions are proposed to maintain the validity of the qualification status during the period of operation license extension.