Nucleotide import is critical to the reverse transcription and thus a key step in the life cycle of HIV-1 virus. In this work, boosted by the recently determined atomic structure of the whole HIV-1 capsid and our understanding of its dynamics, we carry out a computational structure-based study of the mechanism of nucleotide import by HIV-1 capsid. Our analysis reveals a number of novel insights into the mechanism. Specifically, our structure analysis indicates that arginine 18 side chains use a bind-translocate-release mechanism to bind and guide the long nucleotide to pass through the arginine ring before releasing it into the capsid. We discover that LYS 25 plays a critical role in defining the directionality of the transport, in facilitating the disassociation of nucleotides from the arginine ring, and in relaying them further into the interior of the capsid. We predict that mutations of LYS 25 to other residues, assuming that they still result in viable viruses, should reverse the directionality of the transport and significantly lower the infectivity.