Based on the law of mass conservation and the transient profile method used in determining the unsaturated hydraulic conductivity of soil, the method for determining the unsaturated dispersion coefficient of soil was developed. It was shown by field experiments that the method was effective in estinnating unsaturated dispersion coefficient under field condition, even for heterogeneous soils or those of spatial variability in their properties. The method has two advantages, i.e. simplicity in experimentation and computation and values of D and V and their relationship for a group of plots being able to be obtained from an experiment. Modelling experiments have shown this method is, reliable.