Abstract: Abstract : C-N Metabolic Characteristics in Leaf and Starch Accumulating Developments in the root tubers of cassava during in Cultivars with Different starch content were studied with 3 cassava varieties(SC201,GR891, nanzhi199)in this experiment. The results showed that from the root tuber setting stages to the ripping stage,it had an positisive correlation between Starch content of tuberous root, GS activity of leef ,SPS activity of leef, SS activity of leef and Total soluble sugars content of leef，but it had an significant and positisive correlation with SS activity of leef. And it had an negative correlation with NR activity of leef. But it showed an high opposite negative correlation between Sucrose content of leef, Total soluble sugars content of leef and Amino acid content of leef during the same time. It showed that“Source”had strong supplying ability of assimilating matter in high starch content ones. Three cassava varieties had the same discipline.