A new cadmium(II) coordination polymer, [Cd(TITMB) 2]-(SO 4)·21H 2O, where TITMB=1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene, was obtained by self-assembly of tripodal ligand TITMB with CdSO 4·2.7H 2O in acetonitrile, and characterized by X-ray crystallography. The crystal data belongs to monoclinic space group C c with cell parameters a=1.16891(4) nm, b=2.06671(6) nm, c=2.48185(7) nm, β=97.8560(10)°, R=0.0487, wR=0.1211. The results of structure analysis indicate that each TITMB ligand coordinates three metal atoms and in turn each Cd(II) atom with octahedral coordination geometry connects six nitrogen atoms of imidazole group from six different TITMB ligands to produce a 2D honey~comb network structure. There are a lot of water molecules linked by hydrogen bonds and occupied the channels formed intra- and inter-sheets.