Abstract: In an attempt to finding a way to treat the dye-house wastewater more efficiently, a new type water treating agent ammonium molybdate modified bentonite was prepared with Ca-bentonite as raw material and ammonium molybdate as modifier and was used to treat the wastewater resulting from dyeing with basic blue dye. The optimal preparation conditions were derermined through experiments: turbidity ratio is 1：15，mass fraction of ammonium molybdate solution is 0.2%, the soaking and heating time are 5min and 10min respectively. Because dispersed state of bentonite in the water was changed by ammonium molybdate，its adsorptive capability and ionic exchange ability were improved, and its color removal rate from the wastewater of basic blue dye was 96.53%. On this basis, the adsorption isothermal line of the modified bentonite was set，which belonged to L-model，and the bentonite’s adsorption of the basic blue dye is coordinated surface adsorption.