Abstract: The Annual runoff of four main rivers in Aibi Lake watershed is analysized by statistical approach. The result obtained is that they have certain dry-watery year cycle, and the weak tendency of increase or decrease, and also the little decreasing tendency of their composition. Therefore the great contraction of Aibi Lake does not Result in the runoff change, but in the human activities During the period of relately stable Aibi Lake the change of it is mainly subjected to the natural runoff change