The dispersion phenomena of the Floquet-Bloch waves in Periodic dielectric structures are analysed and summarized in terms of the wavevector diagrams. It is shown that the formation and variation of the stop-bands in wavevector diagrams are strongly dependent on the light wavelength and the structural parameters. With the increase of the periodic length or with the decrease of the light wavelength, the wavevector diagrams become more complicated,and more stop-bands would appear.