The content, chemical composition, and structure characteristics of the humic acid in organic fertilizers with different C/N materials were analyzed using potassium dichromate volumetric method, elemental analysis, Fourier transform infrared spectroscopy and solid state 13C nuclear magnetic resonance technology. The humic acid in the organic fertilizer containing four different C/N materials is mainly composed of free humic acid that accounted for more than 98%. The content of total humic acid and free humic acid increased and water soluble humic acid reduced with an increase of C/N ratio and such a change was not significant when C/N ratio was in the range of 25 - 30:1. C, H, O, N and other elements were the main components in the humic acid in the four organic fertilizers. The humic acid structure is mainly constituted of aliphatic carbon, oxygen containing aliphatic, aromatic carbon and carboxyl carbon, carbonyl carbon etc. Differences in functional groups in different C/N organic fertilizers were observed. The organic fertilizer with a carbon-nitrogen ratio of 20:1 contained more carbohydrates (or polysaccharide) and carboxylic oxygen than other organic fertilizers with different carbon-nitrogen ratios.