Formic acid (FA, HCOOH) is one of the most promising hydrogen carriers. Developing cost-effective dehydrogenation catalyst for formic acid is the key to the application of formic acid as hydrogen storage compound. In this study, we systematically studied the catalytic performance of nitrogen-doped graphene supported Pd₁ single-atom and Pd₄ single-cluster for dehydrogenation of formic acid by density functional theory calculations. Three types of nitrogen-dopants (pyridinic N, pyrrolic N and graphitic N) were introduced into graphene to determine which N dopant plays an important role in catalytic dehydrogenation of formic acid. The results showed that HCOOH decomposition proceeds via the formate (HCOO) intermediate to yield product CO₂ and H₂, so all catalysts have 100% H₂ selectivity. On graphN3 support, the catalytic activity of Pd₄ single-cluster catalyst (SCC) is better than that of Pd₁ single-atom catalyst (SAC), while on pyriN3 and pyrroN3, the catalytic activity of Pd₁ SAC is better. Compared with traditional Pd (111), the present SACs and SCCs exhibit higher HCOOH dehydrogenation activity, and Pd₄@graphN3 has the best catalytic performance with an energy span of 0.75 eV, much lower than 1.33 eV of Pd (111). Our work provides an insight into the effects of the coordination environment of N-doped graphene support and active center size on FA dehydrogenation performance.