Abstract: The Principles Relevant to the Use of Nuclear Power Sources in Outer Space has been passed for 20 years. Although the Principles are only part of the scope of the resolution of the United Nations and their legal binding does not extend to the international conventions, the content involved in the Principles is not only about the general nuclear safety, but also related to the exploration of outer space and the orderly and healthy development. The status and role of the Principles are becoming more important with the development of the space, especially with the increasingly deeper construction of the international community on nuclear safety mechanism, so its importance of being a basic specification file in this area is self-evident. It is both meaningful in theory and practice to analyze the Principles-possible trends by re-examine its background on the basis of 20 years of implementation and experience, meanwhile, it also can theoretically pave way for the establishment of China's future space nuclear use and nuclear safety mechanism.