The first batch of spent reactor fuel transport casks manufactured in China have reached their life span, and there is no precedent of life extension approval for this type of cask in China before. Therefore, in order to ensure that the containers with extended life still meet the requirements of laws and standards, the work aims to give the evaluation method and example of studying the life extension of spent reactor fuel transport casks. The evaluation of design life extension was divided into the evaluation for this type of cask and the evaluation for each cask. The evaluation results met the requirements in both aspects, which proved that the cask with extended life was safe and feasible. Through the test and evaluation, this batch of cask met the requirements, and the life extension of the cask was safe and feasible. In addition, a mechanical test was designed for the life extension of the cask, and the theoretical analysis was carried out, of which the results were consistent with the test results. An effective method is proposed to evaluate the life extension of small spent fuel transport cask. With the method provided in this study as the main line, together with the life evaluation of special functional materials and important structures of large casks, it can provide important reference for the life extension evaluation of spent fuel transport casks in large commercial nuclear power plants.