This study examined the decisive causes for North Korea’s failure in the rapid and decisive achievement of victory in the beginning of the Korean War, focusing on the concept, characteristics and operation methods of maneuver strategy from the military strategic point of view. North Korea made use of maneuver strategy for the rapid and decisive achievement of victory in the beginning of the Korean War, but did not accomplish the goal, and the causes are summarized as follows: First, it avoided the enemy's strong points and did not attack weak points. In a maneuver strategy, the attack on the enemy’s weak points is crucial for operational success, and the North Korean Army at the time strongly attacked the strong points of the South Korean defense system strongly while it attacked its weak points weakly. Second, it failed in achieving a dominant position of the tempo of maneuver through a breakthrough in depth. The annihilation of the South Korean main force in the north of Suwon, the core goal of North Korean Step 1 Operation was possible only if it succeeded in breakthrough in depth in Chuncheon and Hongcheon areas. However, Chuncheon and Hongcheon areas were selected as the North Korean army’s direction of supporting the attack, so tank forces, the core bases for the execution of operations of North Korean Army were not assigned and this became the main cause of failure in breakthrough in depth. Third, it failed in the sequential execution of operations. Even though the annihilation of the South Korean main force by grand siege in north of Suwon became more difficult due to the failure in in-depth breakthrough in Chuncheon and Hongcheon areas, but if an attack was made continuously on the South Korean force whose battle line collapsed by powerful attacks in the Seoul area, its decisive victory might be achieved. However, as the North Korean Army failed in securing the Han River Bridges early, it failed to connect the sequential execution of operations from Step 1 to Step 2 and wasted five days to get over the Han River line, and consequently it lost these opportunities. In other words, North Korea pursued a maneuver strategy through a lightning war for rapid achievement of victory, but it did not apply the characteristics and operation methods of the maneuver strategy properly throughout the whole process of war plans and the conduct of war, which is the biggest military strategic cause for North Korea’s failure in achieving rapid and decisive victory in the beginning of the Korean War.