Abstract: The synthesis, thermal stability and scale inhibition behavior of polyaspartic acid, a new type water treatment agent, are discussed in this paper. Several conclusions have been drawn: The process of synthesizing polyaspartic acid from Laspartic is simple. The raw material, synthetic process and the application of polyaspartic acid all could do no harm to environment and body. The polyaspartic acid can be applied widely in high temperature water system due to its excellent thermal stability. The ideal inhibition behavior for calcium carbonate can be achieved with polyaspartic acid even at its low dosages. The inhibition rate is up to 88% at the dosages of 0.2 mg/L and 100% at 2.0mg/L. The decreasing tendency of inhibition rate with increasing Ca2 concentration could be slowed by increasing polyaspartic acid concentration, and polyaspartic acid is perfect to be applied in high Ca2 concentration water system.