The effects of molecular weight and compositions of polyacrylates, i.e. sodium homopolyacrylates and modified polyacrylates on their tolerance to calcium ion (CaV), dispersancy and flocculence were investigated. The optimum formulations of phosphate-free detergent powder containing the polymers as substitute of phosphate in detergent were obtained by orthogonal test. By increasing the molecular weight of homopolyacrylate in testing range, their CaV are enhanced dramatically and the dispersancy are decreased but still are better than that of sodium tripolyphosphate (STPP). The modified polyacrylates were copolymerized with maleic anhydride (MA), methyl acrylate(AM) and acrylic acid (AA) with different compositions. The composition of copolymer affects its CaV slightly. By increasing the molecular weight in testing range, their CaV are enhanced moderately and the dispersancy of copolymer are slightly decreased. The flocculence of the polymer is enhanced by increasing the molecular weight, and is not related to type of the polymer but CaV of the polymer.