Graphdiyne-based nanotubes (GDNTs) are a novel type of carbon nanotubes. While conventional carbon nanotubes (CNTs) aregenerated by rolling graphene sheets, GDNTs are generated by rolling sheets that are similar to graphene but where the edges areelongated by the introduction of additional acetylene bonds between vertices (C6 aromatic rings). Such nanotubes are predicted tohave many useful practical applications, but a thorough understanding of the relationship between their structure and theirphysical properties is still missing. We present a theoretical study of the electronic and optical properties of GDNTs. Thestructural, electronic, and optical properties of GDNTs with different diameters (i.e., 2–10 additional acetylene bonds) havebeen studied systematically by using density function theory (DFT) and self-consistent charge density functional tight-binding(SCC-DFTB) and by solving the Bethe–Salpeter equation (BSE), with and without considering the electron-hole interactions.The results indicate that the GDNTs are semiconductors with the direct band gap in close range, which is beneficial forphotoelectronic devices and applications. Moreover, the absorption spectra of the GDNTs with different edge structures, (armchair,and zigzag) revealed little differences between the optical spectra of armchair and zigzag GDNTs, which could mean thatfine separation between those structures (a process that is likely difficult and expensive in practice) will not be necessary.Importantly, the nanotubes were highly stable based on their cohesive energies, and their exciton binding energies were as largeas about ~ 1 eV. From a methodological point of view, SCC-DFTB was found to be in agreement with more elaborate DFTcalculations for most systems.