A water-swellable rubber (WSR), compatibilized by the amphiphilic block copolymer, has been prepared by blending a natural rubber (NR) matrix with crosslinked sodium polyacrylate (CSP), poly(ethylene oxide)-b-poly(butyl acrylate) (PEO-b-PBA), poly(ethylene glycol) (PEG), reinforced filler, and vulcanizing agents. The preparation process was described. The microphase structure of WSR was characterized by a scanning electron microscopy (SEM) photograph. The dependence of the degree of the water-absorbing and the water-swelling, the water-absorbing and water-swelling rates on CSP, PEG, and PEO-b-PBA contents were investigated, The compatibilizing mechanism of PEO-b-PBA on WSR was studied. And the optimum composition range was identified: CSP (30-60 phr), PEG (10-20 phr) PEO-b-PBA (PEO/PBA = 0.36, 5 phr).