Abstract:     Over the past few decades, interdisciplinary research is widely considered a hothouse for innovation, and has garnered much attention within the scientific and academic communities. In fact, interdisciplinary research has become so popular that many universities are establishing interdisciplinary programs, and many countries have established various support programs to encourage interdisciplinary research. 
    Therefore, monitoring the evolution of interdisciplinary research is of great importance to help R&D scholars in their exploration of opportunities for interdisciplinary research, provide rationales for policy aimed at fostering interdisciplinary research as well as for policy direction corresponding to the future trend. Based on the fact, that technology convergence starts with convergence in science, it may be helpful to provide policy-makers clues with respect to furthering technology convergence that is potentially driven by science convergence. Along with these scientific and social attentions to interdisciplinary, academic research in interdisciplinary has shown a fast growth recently. However, very few studies have assessed the evolution of interdisciplinary over time. Our study attempts to fill this gap.
    Based on the reliable and complete enumeration of paper data covering a 15-year period from the three countries, this study offers an in-depth comparative analysis of the evolution of interdisciplinary research among China, the USA and Japan. The results of our analysis suggest the following. First, the results confirm that interdisciplinary is a present feature of the current scientific innovation system in the three countries. And the absolute number of interdisciplinary papers in China has increased faster than in the USA and Japan. But the proportion of inter-divisional papers to interdisciplinary papers in China has declined in recent years. This implies that Chinese researchers should be encouraged to break down disciplinary barriers and promote convergence between more distant disciplines. These may produce more potentially fruitful outputs. Second, among all the interdisciplinary papers, more than 60% stem from two disciplines in the three countries. In addition, the proportion of convergence from more than two disciplines is higher in China than in the USA and Japan. Therefore, more opportunities for interdisciplinary in the future may come from combinations between more diverse disciplines. Third, our intuitive mapping of interdisciplinary network evidently describes the location of convergence in scientific disciplines. The interdisciplinary network characteristics show that network connectivity, cohesion, and average degree of China are lower than those of the USA and Japan. Furthermore, this paper investigates prominent discipline fusion combinations. The major discipline fusion combinations are different among the three countries. In addition, engineering sector occupies an important position in the interdisciplinary research of China. These results imply that apart from the initiatives that interdisciplinary research of China should cover and promote convergence between scientific disciplines, strategic planning for interdisciplinary through the quantitative monitoring of interdisciplinary of the other countries may be achievable.
    However, our study also has certain limitations. First, interdisciplinary relationships can be studied at different levels, including papers, journals, research projects, etc. In this study, only papers of the three countries are analyzed. Second, different classification criteria of discipline may result in different results.

Key words: interdisciplinary, inter-divisional convergence, bibliometric analysis, social network analysis