Since the reform and opening-up in 1978, opening-up and international S&T cooperation have greatly promoted the development of China's science and technology. Through historical investigation and case studies, this paper discusses the role of opening-up and international cooperation in China's science development in three aspects: Science progress, institutional learning and the introduction of ideas, and it shows that opening-up and international cooperation have not only helped China make great progress in science, but also brought about new ideas and vision, and promoted the reform, institution building and policy progress of China's science and technology system. This paper summarizes the experience of historical development and puts forward several aspects that need to be strengthened in the future development.