With the advancement of carbon neutrality and sustainable energy goals, developing environmentally friendly pathways for multicarbon (C2+) product synthesis has become an important research field. 1,3-Butadiene, a key feedstock for synthetic rubber and polymer materials, is traditionally obtained from naphtha cracking or high-temperature dehydrogenation, both of which are energy-intensive and carbon-intensive processes. In this study, density functional theory (DFT) combined with a constant electrode potential model was employed to investigate the electrochemical reduction of ethyne (C2H2) to 1,3-butadiene on Cu(100). The results reveal that the main reaction pathway involves hydrogenation of adsorbed ethyne to form *C2H3, followed by *C2H2 - *C2H3 coupling and a subsequent hydrogenation step to yield the product. Strain engineering analysis indicates that compressive strain along the coupling direction facilitates C-C bond formation in the *C2H2 - *C2H2 coupling process. A comparison of different metal catalysts reveals a scaling relationship between activation energy and adsorption energy, where weaker adsorption corresponds to higher reactivity, indicating that adsorption energy can serve as an effective descriptor for high-throughput screening. This work not only elucidates the mechanism of ethyne conversion selectivity to 1,3-butadiene but also provides strategies to enhance coupling efficiency, offering theoretical guidance for the design of efficient catalysts and sustainable chemical synthesis.