Abstract: In recent years,exporting countries such as Russia often suffer from disruptions in natural gas export supply due to natural disasters, economic, political and military factors. Once the natural gas export supply security problems occur, not only the importing countries suffer enormous economic losses, the interests of the exporting countries will also be severely damaged. So gas export supply security is an important aspect that should be highly valued by the exporting countries. On the other hand, gas import for some countries such as China has risen steadily during this period. In the process of rapid development of natural gas market, the natural gas infrastructure has been improved significantly, but it is still a key factor which restricts its gas consumption. Therefore, importing countries should pay more attention to the construction of natural gas infrastructure. In this context, a dynamic game problem characterized by natural gas importing and exporting countries with conflicted interests is studied, with focus mainly on a perspective of supply security abroad and domestic infrastructure.
Specifically, in the first section of this paper, the main players, objective functions and strategy sets are discussed, and a dynamic game model is established to reflect the importing country's economic objective and the exporting country's supply stability and economic consideration. The second section uses the optimal control theory to study the optimal strategy of the optimal sales price and infrastructure investment in the importing country, and the optimal production strategy for the exporting country. The third section mainly analyzes the optimal export price under different market scenarios. Results show that, a higher export price will lead to a higher domestic sales price and a less infrastructure investment. The exporting countries' effort has a form of inverted "U" in relation to export price. Export prices, export supply security, infrastructure stock and utility of the exporting country are higher, and utility of the importing country is lower in an exporting monopolistic market than in a monopolistic market. For an exporting monopolistic market, export prices, export supply security, infrastructure stock and utility of the exporting country are higher, and utility of the importing country is lower in the case of negotiation than in the case of cooperation.

Key words: export supply security, domestic infrastructure, natural gas import and export, optimal control