Based on analyzing the characteristics of flow through large soil pores and the transport and transformation mechanisms of volatile contamination

a two-region model for volatile contamination transport and transformation in soil is established; and a numerical solution of this model is qiven; and the behaviors of volatile contamination suck as volatility and absorption etc. in soil are described quantitatively. Taking heptachlor for example and simulating its dynamic transport and transformation behavior in soil

it is concluded that the volatility of pesticide and the water content of immobile region are key factors affecting the concentration distribution of pesticide; and that the volatile mathematical model of pesticide used in the two-region numerical model in soil can more reasonably manifest its behavior mechanism. The study is of significance for predicting and restricting pesticide pollution.