Abstract: Estimating solute transport parameters with boundary layer method is a reliable and simple method,but how to determine the position of the boundary layer is the key factor to limit its the application.Because the boundary layer of the brilliant blue dye in soil is very clear and easy to be determined,the feasibility of indicating the boundary layer of Cl^- using the brilliant blue dye is studied in this paper.The results show that the transport law of the brilliant blue dye is similar to that of the Cl^-.The relationship between the boundary layers of the Cl^- and the brilliant blue dye can be described by the linear-equation under the condition of the relatively small value of dispersivity.Furthermore,the relationship between the boundary layers of the Cl^- and the brilliant blue in sand soil and light loam soil could be derived,which will provide an idea to use the brilliant blue dye to indicate the boundary layers of the non-reactive solutes.