A new chitosan copolymer (CEC) was successfully synthesized by chitosan (CTS) and acrylic acid (AA) as monomer and ammonium persulfate (APS) as initiator, which copolymerization under 2% (volume fraction) glacial acetic acid solutions. The chitosan derivative was characterized by FTIR, 1H NMR. According to scale inhibition performance, the optimal synthesis conditions of CEC were selected by single factor tests, which were as follows: the mass ratio of AA: CTS was 5.30: 3.00, the reaction temperature was 75 ℃, the reaction time was 4 h and the APS mass fraction was 3%. The scale inhibition performance in secondary municipal wastewater treatment of CEC was studied and the results presented that CEC exhibited excellent inhibition performance to CaCO3 and the scale inhibition rate could reach 92.93% in the presence of 30 mg/L of CEC, which was significantly better than comercial scale inhibitor 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP). The resistance mechanism to CaCO3 was investigated by SEM and XRD, and it could be noted that the mechanism of CEC on CaCO3 was mainly lattice distortion.