A novel amphoteric polycarboxylic acid-based superplasticizer (APC) was prepared by solution copolymerization from maleic anhydride (MA), allyl polyethylene glycol (APEG) and dimethyl diallyl ammonium chloride(DADMAC). The cationic monomer DADMAC was introduced for improving the performances of sulphoaluminate cement (SAC) with APC. The condition on preparation of APC was determined by the orthogonal experiment. The flow of paste and mortar were alao assessed. Results indicated that APC could improve the fluidity of paste and motar with APC. Zeta potential measurements indicate steric repulsion between the cement particles carrying adsorbed polymer molecules is the main mechanism for dispersion.