The infrared spectra of PrBa2Cu3O6+x (x=1, 0.3) ceramics and films with c-axis orientation are reported in this paper, and the phonon modes in c-axis and ab-plane are distinguished by treating the different vibrational behaviour for film and ceramic samples. Due to the fact that PrBa2Cu3O6+x possesses the similar crystal structure as RBa2Cu3O6+x (R=Y and other rare earth elements), by comparing the phonon spectra, espeacially the B1u (x=1), Eu and A2u (x=0.3) modes of Pr, Y and other rare earth elements, it is found that the valence value of Pr depends on the oxygen content, i.e., the Pr valence is 3+ in PrBa2Cu3O6.3 while it is larger then 3+ in PrBa2Cu3O7.