Based on the citation data of 52 sample countries and regions around the world, this paper analyzes the internal mechanism of international knowledge flow from two perspectives of individuals and pairs of countries; and then uses the negative binomial regression model to test the key factors influencing the performance of national knowledge flows and the inter-country knowledge flows. The results showed that: (1) the effect of international cooperation on national knowledge flow performance under different time-lags is different. (2) Knowledge gap, knowledge similarity, international mobility, collaboration strength and network location of inter-State relations are all important factors affecting inter-country knowledge flows. And there is a path of action, that is, the network location of inter-State relations - knowledge gap - knowledge flow. Therefore, when China participates in the global knowledge flow, on the one hand, it needs to continuously establish the scientific and research cooperation relationship, utilizing favorable conditions in the process of searching for potential partners based on knowledge similarity and the flow of talent; on the other hand, it should build up the knowledge exchange platform between countries based on the similar network locations to help promote knowledge gap positively affects international knowledge flow.