On July 12, 2016, an arbitral tribunal established under Annex VII of the United Nations Convention on the Law of the Sea (UNCLOS) issued a significant decision on the South China Sea dispute, which has triggered discussions on many legal issues and provided a legal basis for countries’ activities in the South China Sea. The ruling was seen as a victory for the Philippines over China and served as the basis for subsequent countermeasures against China by neighboring countries. In 2021, in addition to the U.S. continuing to send warships to sail the South China Sea, many other countries have responded, and China has countered with drills and other actions. With conflicting philosophies and frequent actions from all sides, it is no doubt that the tensions in the South China Sea will be exacerbated. This publication aims to discuss the actions of relevant countries in the South China Sea and their impact on regional security. First, it will explain the conflict between the U.S. and China in establishing the South China Sea order; then, it will explore the actions of the U.S.-China-led countries in the South China Sea and the participation of extraterritorial countries; finally, it will discuss the impact of the aforementioned countries’ frequent actions in the South China Sea on the Indo-Pacific region.