Abstract: In this experiment, use PH control method to synthesize the sodium polyacrylate of lower molecular weight, acrylic as a monomer, potassium persulfate as the initiator, n-dodecyl mercaptan as chain transfer agent, Sodium carbonate as PH control agent, synthetic products were characterized by IR and the description was sodium polyacrylate, and the sodium polyacrylate viscosity measured by viscosity-average molecular weight of about 680, lower sodium polyacrylate successfully synthesized. According to national standards (GB/T 16632-2008) testing Scale inhibitive performance of lower molecular weight sodium polyacrylate:With ultra-low molecular weight sodium polyacrylate added amount, the effect of increasing scale, when the amount of 1.00 g·L^-1, the inhibition rate reached 95%.