Abstract: During the Second Sino-Japanese War, despite sharing the same anticipation of protracted war, the Kuomintang (KMT) and the Chinese Communist Party (CCP) had absolutely different estimates for the duration of the war. Believing that the duration depended on the condition of both sides and the collaborator, Mao Zedong rarely made specific estimates. Only in 1942, the CCP delivered a misjudgment according to the situation of Europe, but corrected it in time. Except for the balance of power between both sides of the war, the CCP also paid attention to the one between the KMT and itself. The CCP was making consistent efforts to change its role from a “morale booster” to a leader, which was influential in the progress of the war and even in the development of China after the war. In contrast, as the KMT’s interpretation of protracted war did not include concrete division of different phases, the strategic analysis only ended up as a variant of the KMT’s quick victory anticipation. From year to year, the KMT’s optimistic prediction failed to come true. Meanwhile, the political and military condition of the Nationalist Government did not improve as expected. As a result, the KMT lost advantage in the competition with the CCP gradually.