Abstract: International space cooperation can be categorized variously according to different classificationstandards. The "Declaration on International Cooperation in the Exploration and Use of Outer Space for the Benefit and in the Interest of All States, Taking into Particular Account the Needs of Developing Countries" puts forward eight guiding principles for the international space cooperation, which may provide not only the technological and financial assistance but also legal guidance for the long-term sustainability of outer space activities and thus is very important. However, in the work of seeking the long-term sustainability of outer space activities, the international cooperation of space-faring countries is very often affected by the international political situation and is carried out without not only the regulation of international treaties or customary laws but also the implementation and supervision of international organizations or organs. Consequently, the resolution of the issue of long-term sustainability of outer space activities has to rely primarily on the Guidelines for the Long-term Sustainability of Outer Space Activities, but there are some limitations about the provisions of international cooperation in the Guideline 23. In this sense, international community may seek to strengthen the international cooperation in the field of space technology, law, finance and organization in order to achieve the long-term sustainability of outer space activities.