The infrared refleotion spectra of Y1-xPrxBa2Cu3O7+δ(x = 0,0.1,0.2,0.4,0.5, 0.6, 1.0) are measured in the temprature range of 4.2 to 300K. The measurements show that Ba mode has double mode behavior, the strength of which inverses with increasing x, and that the position of the reflection peak at 194cm-1, which has been identified as Y mode of YBa2Cu3O7+δ, is indenpendent of the density of Pr, i. e, the position of the peak does not change whether the Y is partially or totally substitued by Pr. This indicates that in Y1-xPrxBa2Cu3O7+δ the valence of Pr is tetra-valent. The substitution of Pr make the mobile holes localize around Pr, thereby lead to the suppression of superconductivity.