In order to establish forecasting the unity of cassava stem leaf biomass mathematical model. This study investigated five cassava varieties, stem base and middle and upper stem diameter and stem base to branch of stem length and in the branch of various branches diameter, length, etc. And the stem and branches biomass were divided into two parts, this paper probed into the two parts with relevant morphological indexes of biomass relationship. Through a variety of model fitting compared. In the end, gained a cassava estimating model of stem-leaf biomass by simulating model and choosing was to be the best. Including RMSE was 104.2, correlation coefficient was 0.9110, fitting effect was good. And this model than their predecessors fitting results of mathematical model has better fitting effect.