Graphdiyne (GDY) is a new carbon allotrope, composed of sp- and sp(2)-hybridized carbon atoms, which has a larger specific surface area and a unique pore structure in comparison with graphene. Based on a first-principles analysis, the effect of Ti modification on the adsorption of methane (CH4) by a GDY system was studied. The results indicated that modification with a Ti atom can significantly improve the CH4 adsorption properties of GDY. The macropore position on the alkyne chain is the most stable adsorption site. A GDY system modified using a single Ti atom (Ti-GDY) can adsorb 16 CH4 molecules on both sides, and the average adsorption energy can reach -0.225 eV/CH4. Furthermore, a GDY system modified using two Ti atoms (2Ti-GDY) can adsorb 24 CH4 molecules. The average adsorption energy is approximately -0.223 eV/CH4, and the CH4 storage capacity is 55.24 wt %. In the system, Ti and GDY are mainly connected by 2p-3d interactions between the C and Ti atoms. Hybridization between the CH4 molecule and the substrate, in addition to the is H and 3d Ti orbitals, also includes electrostatic interactions. The Ti atom is in a unique macropore position along the alkyne chain, providing sufficient adsorption space and adsorption sites for CH4. The positive electroconductivity of the CH4 surface decreases after adsorption, reducing the influence of repulsion between the CH4 molecules and inducing strong electrostatic interactions with the negatively charged GDY, all of which are beneficial for increasing the amount of adsorption.