Security Dilemma is a basic concept for Western international relation theory to explain global intense, opposition, and reason for conflict forming. As nations see each other as a threat and considered to be against itself is a reaction to the movement of the other side. On the country, the movement of the other side is considered to be a intention of one side to attack each other. Thus, .under the situation of twisted interaction, both sides have increase their cognition of aggression. Oppositely, the countermeasure to protect themselves has become more and more, making the situation moving like spiral. The uncertainty of each other’s intentions and every actions each other took because of the sense of insecurity, which amplify the hostility cognition to each other. Thus, Inimical Spiral has ascended and the ascension is the main cause of Inimical Spiral.

The main purpose of this theory is to discuss the possibility of China and Japan to form security dilemma. Especially on adjustments of American security strategy, the change of security role of Japan, and the change of national policy of China, which all affect Sino-Japnese Relationships after 911 attack. Based on this reason, the theory is try to explain three questions below.
1.What’s Japan’s perception of the rise of China after 911 attack? And how does the perception influence its national security policy?
2.What’s China’s perception of goal of Japan’s ordinary state? And what’s it reaction to the changes of Japan’s national security policy after 911 attack?
3.Whether trying to analyze China and Japan’s understanding to each other’s behavior would cause Security Dilemma? And whether Sino-Japnese Relationships are competition or corporation in the future?