The crystalline structure refinement, chemical bond ionicity, and lattice energy were carried out for Zn(Ta1-xNbx)2O6 ceramics with tri-a-PbO2 structure to investigate the correlations between the crystalline structure, phase stability, bond ionicity, and microwave dielectric properties. The chemical bond ionicity and lattice energy of the ZnTa2O6 system were calculated and evaluated using a semiempirical method based on the dielectric description theory proposed by Phillips, Van Vechten, and Levine (PVL theory). The crystalline structure stability varied with the content of Nb5+ ion resulted in the lattice energy decrease. The increase of Ta/NbO bond ionicity was observed in the crystalline structure, which should be main contribution to electric polarization. The dielectric properties of the Zn(Ta1-xNbx)2O6 ceramics were strongly dependent on the chemical bond ionicity of Ta/NbO bond with tri-a-PbO2 structure.