The ROK-China conflicts due to the THAAD deployment in South Korea and the Trump administration’s preemptive strike doctrine toward the DPRK have put the security of the Korean Peninsula in a grave state. At the same time, positive expectations for ROK-DPRK-U.S. talks have been growing recently. However, since whether the United States will conduct a preemptive strike or not depends on the results of the U.S.-DPRK talks, the security of the Korean Peninsula is in a precarious state. This paper, therefore, attempts to analyze the Sino-North Korean Mutual Aid and Cooperation Friendship Treaty (hereafter referred to as the Sino-North Korean Friendship Treaty) that will allow for the reconsideration of China’s role in nullifying the uncertainty on the Korean Peninsula according to the treaty. The Automatic intervention, according to Article 2 of the Sino-North Korean Friendship Treaty, is an exercise of the right of self-defense that can be implemented when the requirements of necessity and proportionality of Customary International Law are met, and only until the UN Security council takes appropriate measures, according to Article 51 of the UN Charter. China’s intervention in the case of contingency on the Korean Peninsula, according to the Sino-North Korean Friendship Treaty, has limitations with regards to compliance with Articles 48 and 103 of the UN Charter. It is a special treaty based on the historical background between North Korea and China. Also, since China recently adopted “non-alignment” as a foreign policy, it is unlikely that the Sino-North Korean Friendship Treaty will continue after the regime transition.