The effect of litter decomposition including Suaeda glauca, Phragmites australis, and Spartina alterniflora in Jiaozhou Bay coastal wetlands on the soil organic carbon mineralization was investigated using three-dimensional fluorescence spectroscopy (3D-EEMs) in laboratory. Addition of litters improved the mineralization rate and the cumulative mineralization of soil organic carbon, which decreased in the order of Suaeda glauca > Spartina alterniflora > Phragmites australis > control. The power curve model effectively described the trends of mineralization rate and the cumulative mineralization of soil organic carbon. Spectral analysis revealed that the fluorescence intensity of proteins was greater than that of humic acid during decomposition of litter. Fluorescence integration was performed for qualitative analysis, and the results showed that the proportion of aromatic protein substances was the highest, followed by the humic substances under different treatment conditions. Fluorescence parameters indicated that the degree of aromatization of soil organic carbon first increased and then decreased during the incubation period. Litter decomposition enhanced the soil microbial activity by increasing soil nutrients, which altered the structure and chemical composition of organic carbon in soil. In addition, the vegetation characters determined the degree of influence of litters on the soil organic carbon mineralization.