A type of benzoic acid end-capped ploy(ester-imide-ether) (PEIE) block copolymers was synthesized by melt polycondensation from polytetrahydrofuran diol (PTMG), 1,4-butanediol (BD), benzoic acid (BA) and a diacid monomer which was synthesized of trimellitic anhydride (TMA) with para aminobenzoic acid (PABA). The structures and properties of the copolymers were investigated by FT-IR spectroscopy and Ubbelohde viscometer, DSC and TGA. Some properties of the copolymer fibers such as breaking strength, breaking elongation and elasticity were also measured. The result demonstrated that the adding of BA can effectively reduce the inherent viscosities of PEIE. Especially the breaking strength, elastic recovery and heat stability of the fibers are improved obviously when adding 1 % (of the multiblock copolymer weight percentage) BA end capping agent.