The paper put forward a coupled mathematical model of element desorption,transfer and root uptake of heavy metals in soilplant systems,and gives the theoretical quantitative relationships between the plant uptake,on the one hand,and soil solution concentration,soil buffer power,diffusion coefficient,total root length,average radius,water transpiration and growth time on the after.The pot experiments showed that the calculated uptake with this model was highly correlated with the actual uptake of cadmium by ryegrass,and the model could be used to predict rather well th0 effective uptake.