Abstract: Calcium bentonite and sodium bentonite are compared and selected through tests. The slurry mass fraction is chosen to be 10%, and the sodium bentonite of 24 h expansion time is chosen as residue modifier. Taking Guangzhou Metro Line 21 as an example, targeting the sand-clay mixed formation stratum characteristics, through the soil sample set of sand content gradient and water content gradient, the optimal proportion of residue modifier under various working conditions is obtained. The mixing law of sodium bentonite slurry ratio with the change of sand content and water content in the formation is further summarized, and the function is fit to obtain functional relationship of the three.