Abstract: In order to reveal the color emerging mechanism of maple leaves in Autumn, 3 kinds of Acer truncatum Bunge clones were taken as material. The variations of chlorophyII, carotenoids, anthocyanin and soluble sugar content in maple leaves were measured during the color-changing period from 19-October to 11-November, 2011. The results indicated that: little anthocyanin was contented in the leaves of 3 kinds of maple clones before the color change, which had nothing to do with the following color-changing. The reason for leaves of clone R turn red was not only because of induction of chorophyII and carotenoids, but also the following large production of anthocyanin. The color changing of leaves in different clones of maple trees was apllied to anthocyanin content and pigment proportion and decided by genotype. There was significant difference in the content of soluble sugar in different clones in which clone R was the highest one. The process of anthocyanin production might be induced by the high content of soluble sugar. The carotenoids proportion was highest in clone Y and was lowest in clone R.