Solvothermal reaction of CdCl2·2.5H2O and 1-tetrazole-4-imidazole-benzene (Htzib) yielded a new cadmium(II) coordination polymer [Cd2Cl2(tzib)2]n·nH2O (1), which has been characterized by single-crystal X-ray diffraction analysis. In 1, metal center Cd(II) ions are linked by μ2-Cl and tzib– with μ3-κ3N1:N2:N6 and μ4-κ4N1:N3:N4:N6 coordination modes into a novel 3D structure. Due to the lattice water molecules filled in the closed cages of 1, they cannot easily escape from the 3D framework. Because of this structural feature, polymer 1 displays relative high thermal stability up to ~400 °C. Moreover, luminescent properties and theoretical calculations of 1 are also discussed. Interestingly, tunable ultraviolet-to-visible emissions for 1 are observed.