The phonon spectra of C-15 phase (Hf0.5Zr0.5V2)Hx with five different composition was measured with the Beryllium Filter Detector spectrometer. It was observed that their phonon spectra vary with their hydrogen content. The result shows that the change of Tc of (Hf0.5Zr0.5V2)Hx system with x is related to the softening of their acoustic branches. The softening of acoustic branches seems favourable to the rise of Tc, while the softening of optical branches may restrain its superconductivity transition.