Understanding the trapping and diffusion mechanism of hydrogen in vanadium carbide (VC) precipitates is crucial for exploring the issue of hydrogen embrittlement in steel. Although there is widespread consensus that VC can trap hydrogen, the mechanism by which hydrogen diffuses into VC is still unclear. In this study, we used first-principles calculation methods to study the influence of different spacings of carbon vacancies on the trapping and diffusion of hydrogen in VC. The increase in the number of C vacancies makes it easier for vacancies to trap hydrogen, and hydrogen tend to fill up C vacancies. The diffusion of hydrogen into VC only occurs via neighboring C vacancies at a distance of 0.295 nm (connecting vacancies), leading to a diffusion barrier of 0.63–0.78 eV. This is consistent with experimental results and validates the experimental speculation that the diffusion of hydrogen in VC requires a connecting C vacancy grid.