AbstractAcrylic acid (AA) was grafted firstly onto high density polyethylene (HDPE) by in-situ chlorinating graft copolymerization (ISCGC), so a graft copolymer composed of chlorinated polyethylene (CPE) as backbone and poly (acrylic acid) (PAA) as branched chains was synthesized. And subsequently the preparation of its carboxylated ionmers was studied. This work was focused on discussing the reaction process for grafting AA onto HDPE by ISCGC and the preparing of carboxylated ionmers of CPE. In this paper, the structure of graft copolymer and the ionomer were characterized mainly by FT-IR, gel permeation chromatography (GPC) and graft degree (GD). The influence factors which related to the main and side reactions, including the monomer concentration, chlorine contents of the product, and reaction temperature were investigated. Additionally, effects of these factors on reaction process controlling were described. The aim of above is to investigate how CPE-cg-PAA and its sodium-salt ionomer were prepared.