Ba1+ xMoO4 (-0.03 ≤ x ≤ 0.03) ceramics were fabricated by a conventional two-step sintering technique. X-ray diffraction patterns show that there appeared new diffraction peaks when x > 0, which were identified as Ba2MoO5. The Rietveld refinement results indicate that the unit cell volume is the largest at x = -0.02, because it has the lowest packing fraction and covalency. The far-infrared reflectivity (IR) spectra were fitted and analyzed for calculating the intrinsic properties, which comply well with the data obtained from microscopic polarizabilities and damping coefficient angle. The proportion of each mode in the dielectric response demonstrates that the Ba-O8 polyhedra have a decisive role on the dielectric properties. And based on the Raman modes, the internal relations of the structural-properties were revealed with the changes of Ba2+ content.