This paper studied the distribution of high-Cd-content areas in the Chengdu plain and its genesis based on sample collection and laboratory analysis. In the alluvium of the Mianyuan River and Shiting River basins, there are abundant element Cd. The contents of Cd distributed in the alluvium gradually decline in the order from terrace 1 to terrace 5. And such contents in the alluvium of the two rivers (Mianyuan River and Shiting River) flowing through the Longmengshan Mountains are remarkably higher than that of the other water systems. That high contents of Cd inosculated with the different terraces indicates that it is the result from geological processes as an evident controlling factor. This conclusion is radically different from the most previous studies that attribute this phenomenon to artificial factors.