The hydrogen (H) diffusion process is a crucial issue related to storage of plutonium safely. In this work, first-principles GGA + U calculation is performed to elucidate the hydriding and diffusion behaviors of an additional H atom (H-i) in "perfect" PuH2+x (0 <= x <= 1) matrixes. It finds the value of incorporation energy increases with increasing x. The interaction energies show that an extra H-i atom interacts much further with surrounding host atoms in PuH3 than in other Pu hydride matrixes. The minimum migration paths of a H, atom in PuH2+x,are characterized by the image nudged elastic band (CINEB) method. The H-i atom diffuses in PuH2, PuH2.25, and PuH5 matrixes through directly migrating from an octahedral interstice to its nearest octahedral site with energy barriers of 1.36 eV, 1.15 eV, and 1.59 eV, respectively. Oppositely, the metastable IN-site plays a dominant role for the H, migration into the O-site in PuH2.75. The diffusion path of the H-i, atom in PuH3 is Ip -> I(H)0160 -> ipu path with the lowest migration energy of 0.72 eV, which concludes the H-i has relatively higher mobility in PuH3. These findings provide detailed insight into how the H atom corrodes the Pu metal by connecting H atom diffusion in PuH2, PuH3, and intermediate compositions, which can be great interest for assisting the development of the new nuclear fuel for next generation reactors. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.