Polyaspartic acid/ O-carboxymethyl chitosan graft copolymer (denoted as PASP/O-CMC) was synthesized via the reaction of water soluble O-carboxymethyl chitosan (O-CMC) and polysuccinimide (PSI).The obtained graft copolymer (PASP/O-CMC) was characterized by FTIR and 1H NMR. The static scale inhibition method was used to evaluate the scale inhibition behavior of PASP/O-CMC and PASP against barium sulfate. The experimental results showed that PASP/O-CMC possessed the best scale inhibition property against BaSO4. Inhibition efficiency of PASP/O-CMC reached 93.6%, but that of PASP was only 78.4% when the dosage was 100 mg/L in the experiment. The scale inhibition mechanism of the scale inhibitor against BaSO4 was analyzed by means of environmental scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrical conductivity measurement techniques. And it was found that the scale inhibition was mainly caused by lattice distortion of BaSO4, adsorption dispersion and complexation of the scale inhibitor and Ba2+.