One cadmium(II) coordination polymer [Cd(1,4-NDC)(PPIM)₂]_n (1, 1,4-H₂NDC = 1,4-na- phthalenedicarboxylic acid, PPIM = 2-propylimidazole), has been synthesized under hydrothermal conditions and structurally characterized by elemental analysis, TGA and X-ray single-crystal diffraction. Complex 1 crystallizes in monoclinic with space group P2₁/n, a = 8.8292(2), b = 16.6936(4), c = 16.7869(4) Å, β = 99.701(2)°, V = 2438.86(10) ų, Z = 4, D_c = 1.489 Mg/m³, F(000) = 1112, μ = 0.932 mm^–1, S = 1.076, the final R = 0.0360 and wR = 0.0850. In 1, the 1,4-NDC ligand bridges the Cd(II) to form a 1D infinite chain, which are connected through N–H···O hydrogen bond to form a 2D layer then to an overall 3D supramolecular structure. The time-resolved measurements indicate that 1 shows highly prolonged phosphorescent lifetime about 452 times in comparison with that of pristine PPIM ligand. Single-crystal analysis and theory calculations indicate that strong coordination bonds and complete separation of HOMOs and LUMOs in the rigid matrix of 1 promote the long-last phosphorescence emission.