This paper introduces the effect of viscosifier for drilling fluid and some common viscosifier. And then studies the method of synthesizing polyacrylate sodium (PAAS) from acrylamide (AM), acrylic acid (AA) and sodium hydroxide (NaOH). The author has drawn out a perpendicular experimental scheme with 4 levels and 3 factors after plentiful preliminary tests and synthesized 9 samples. According to samples’ effect on the apparent viscosity of water-based slurry, we choice the best formula. The best formula is that AA takes 54 percent, AM takes 25 percent, initiation takes 1 percent and the temperature is 70 degree. The viscosity rise rate of apparent viscosity reaches to 243.1% when the PAAS take one percent. It has a good viscosity effect.