Abstract: By the end of 1949, Stalin had used every conceivable stratagem in order to prevent North Korea from launching a war of unification against South Korea. But by late January 1950, he suddenly had a change of mind and decided to wholeheartedly support Kim Il sung to achieve this goal. Whether or not the United States would intervene was only a precondition, not the end. To draw U.S. attention to the Far East was the end result, but not the motive. To encourage and promote the Asian revolution was only the superficial phenomenon, but not the shift in Soviet diplomatic strategy. The signing of the Sino Soviet alliance treaty in 1950 meant that the Soviet Union would lose its only exit to the Pacific Ocean and warm water port. Without doubt, this would cause great loss to Soviet strategic interests. As a result, the Soviet Union would lose its strategic backing in Asia. The reason why Stalin decided to support Kim Il sung’s attack on South Korea was that he hoped to regain, or safeguard Soviet tradition strategic prop in the Far East through this military action. No matter what the outcome might be, the military conflict in the Korean peninsula would guarantee Soviet strategic aim as designed by Stalin.