A novel ammonium salt type polymeric antistatic agent (PDSH) was synthesized from methacrylatoethyl trimethyl ammonium chloride, styrene, and 2-hydroxyethyl methacrylate via radical polymerization. Antistatic poly(acrylonitrile-co-butadiene-co-styrene) (ABS)/PDSH composites were prepared by blending PDSH with ABS resin. The results showed that the surface resistivity of ABS/PDSH composites with PDSH addition decreased significantly. The surface resistivity of ABS/PDSH composites containing 20 wt% PDSH was around 109–1010 Ω, which was about 106 times lower than that of neat ABS. At the same time, ABS/PDSH composites had good thermal stability and hydrophilicity. The PDSH was more uniformly dispersed within the ABS resin and had less influence on the mechanical properties of the composites. With the demonstrated properties, the prepared copolymer PDSH can serve as a well-integrated antistatic agent and display potential for the antistatic treatment of ABS.