Understanding the evolution of carbon structure in coal-assisted water electrolysis for hydrogen production (CAWE) is essential for seeking strategies to improve the rate of CAWE and getting more insight into the potential significance of CAWE. In this work, C-13 nuclear magnetic resonance (NMR) is used to make out the evolution of carbon structure in CAWE. First, the electrolysis characteristics of three different-rank coals are revealed using electrochemical methods. Then, before and after electrolysis, the evolution of carbon structure is analyzed. The results show that CAWE is a process of reducing carbon and increasing oxygen, and the accumulation of oxygen-containing groups is mainly owing to the increase of oxygen aliphatic carbons and oxygen aromatic carbons. After CAWE, the aromatic cluster size decreases and increases for low-rank coals and high-rank coals, respectively.