Clausewitz points out that ”war is the continuation of polices in other means” War is always not an independent thing under any condition, and should be regarded as the tool of politics. Only by judging the history of a war through the standpoint of politics can an antinomy be avoided. Qing dynasty's political goals of the war of Tsungar is to prevent Tsungar from extending to make stronger the sovereignty of Qing Dynasty and build up grand unification, and by making a stronger northwest border defense to deter Russia from invading China. This paper aims to distinguish the political relationship between Tsungar and the Qing dynasty through Clausewitz's standpoint, and comprehend the policy of the Qing dynasty toward Mongols. This study also reviews the effect of Qing-Tsungar war on politics.