Based on the hypothesis that reclaimed water for irrigating is the cardinal source of heavy metals pollution in soil,and the heavy metals are divorced from soil mainly by plant harvest,the article constructsa differential equation and simulates the cumulation of Cd in wheat soil of southeast suburb in Beijing.With the data of relative Cd mass proportion in soil as predictor parameter and in stems and leaves as response ones,the fitting curves are produced respectively.The curves show that the amount of Cd divorced from soil is very small compared with the amount entering into soil via irrigation water.But in the condition of lower concentration in soil,the proportion of Cd divorced from soil is bigger relatively.The prediction shows that the content of Cd will exceed the national standard of China after 40 years in the condition of the content of Cd in reclaimed water with 10mg·m-3 and mass proportion in soil with 0.1333mg.kg-1,but it should be 100 years if the content of Cd in reclaimed water for irrigation reduced to 5mg.m-3.