Aspartic acid-malic acid copolymer (PAMA) is a new product of modified polyaspartic acid, which is a typical representative of green scale inhibitors. In order to extend application of PAMA, According to the method of static scale inhibition test, complex quantity was selected as the evaluation standard. The complexation properties of PAMA towards the Ca2 in supersaturated solution of calcium sulfate under different conditions were investigated. Results showed that the addition of Fe3 、Zn2 、Cu2 or their mixed ions contributed to the decrease of complexation property of PAMA, the declines were Ca2 /Cu2 < Ca2 /Fe3 < Ca2 /Zn2 . In the absence of Fe3 、Zn2 、Cu2 , 2mg/L PAMA could reach the optimum complexation quantity of 9.25g/g. While Without Fe3 、Zn2 、Cu2 , 4mg/L PAMA also had a fine complexation property. In summary, PAMA showed an excellent performance on inhibiting the deposition of sulfate scale.