The 1D-chain polymer of [Cu(Ⅱ)3L3(H2O)]n, (H2L=3-(3,5-dichloro-2-hydroxybenzylid-eneamino)propanoic acid) has been synthesized by reaction of 3,5-dichlorosalicylaldehyde, β-alamine and copper nitrate in ethanol solution. The crystal structure was determined by X-ray diffraction method. The crystal structure belongs to mono-clinic system with space group C2/c and cell parameters: a=3.853 7(3) nm, b=0.777 38(18) nm, c=2.656 36(2) nm, β=116.924(2)° and V=7.095 4(17) nm3, Mr=998.85, Z=8, Dc=1.870 g·cm-3 and F(000)=3 992. The two Cu(Ⅱ) atoms are coordinated with four atoms from Schiff base, and another one is coordinated with five atoms. The square bridging links three metal centers through a novel μ-4,4,5 coordination model, which is further assembled into 1D chain coordination polymer. The 1D chain is further constructed a 3D network by strong O-H…O and C-H…O hydrogen bonds. The coordination polymer presents a good thermal stable property through the thermal analysis.