It is a pursuing goal to find an experimental method for determining the aromatic size of aromatic molecules for scientists. It is a new attempt to measure the aromaticity degree of half-sandwich complexes using Raman spectroscopy.The calculations for the geometries optimization, electrostatic forces, stabilization energies, nucleus independent chemical shifts (NICS) and values of the Raman spectroscopy for (η6-C6X6) and half sandwich complexes ［(η6-C6X6)M］n+(X=F~Br, M=Ti~Mn, n=1, 2) were conducted using density functional theory (DFT) method within Gaussian09 process package. The results showed that, for all the (η6-C6X6) and half sandwich complexes, the values of NICS were all negative. These kinds of molecules all were aromatic. There were strong Ring Stretching Vibration Raman Spectroscopic Frequency (RSVRSF) peaks with A1g/A1 symmetric in the (η6-C6X6) and its half sandwich complexes. The RSVRSF values and the absolute NICS values of the (η6-C6X6) and its half sandwich complexes gradually decreased with the order of F, Cl, and Br, showing a highly positive correlation, and the correlation coefficients were above 0.99. It is theoretically predicted that the determination of the aromatic degree is possible by the experiment determination of the RSVRSF values for the (η6-C6X6) and its half sandwich complexes.