With its extremely strong transportation capability and tremendous cost of construction, high-speed railway not only brings rapid and significant effects on geo-economics and geopolitics, but also extends its trade pattern into the domains of international politics and diplomacy. China, Japan, Germany, and France are the major exporters of high-speed railway and all get involved in a keen competition in the international high-speed railway market. From the power and space perspectives of geopolitics and based on the national interests of security, development, and international influence, this article adopts an overlay analysis of the construction conditions, spatial interest pattern of exporting competitors, and China's competitive advantage, to demonstrate the geopolitical space and cooperation methods of China's high-speed railway diplomacy. The conclusions are as follows. First, the priority space of China's high-speed railway diplomacy includes Russia, Kazakhstan, India, Thailand, Vietnam, Malaysia, Indonesia, Australia, South Korea, the United States, and Brazil; Second, China can develop a multi-level cooperation with the United States, South Korea, Russia, Kazakhstan, and Australia. We also suggest that cooperation with other candidate countries should start with pre-engineering projects such as power generation and transmission. It is possible to cooperate with Brazil and Indonesia by pre-project engineering cooperation based on market demand. Third, in addition to cooperate with countries in the priority space, China can provide financial aid to Kyrgyzstan, Tajikistan, Pakistan, Bangladesh, Myanmar, Laos, Cambodia and other countries with careful consideration of the high-speed railway market demand and risk. Finally, considering only the economic interest, other countries with existing railway project cooperation may be the potential high-speed railway cooperators, such as Romania, Belarus, Estonia, Poland, Hungary, and Serbia.