The polyacrylamide/starch-acrylic acid graft copolymer/bentonite composites with different concentrations of the bentonite and starch-acrylic acid graft copolymer were prepared by in-situ polymerization. The influence of the concentration of the bentonite and starch-acrylic acid graft copolymer on the water absorbency was investigated. The water absorbency of 115 g/g could be achieved with the composite composed of 50wt% bentonite, 17wt% starch-acrylic acid graft copolymer and 33wt% polyacrylamide. The excellent absorption and retention performance of the composite makes it potential to be applied in the model of Rain garden.