The membrane-less and biocathode-containing microbial fuel cells (MLBC-MFCs) were used for the electrical energy production from different wetlands, and the corresponding mechanisms were explored based on the characteristics of dissolved organic matters (DOM) in this study. The average voltage output on indoor MLBC-MFCs was 60 mV for the saltmarsh wetland water (SWW), 48 mV for the forest wetland water (FWW) and 71 mV for the FWW supplemented with sodium chloride (FWWS). For the field experiments, as high as 800 mV was obtained from the MLBC-MFCs installed in the forest wetland and the voltage output varying between 200 mV and 800 mV maintained approximately for half a year except for a few days with an extremely low temperature, while the voltage output from the MLBC-MFCs installed in the saltmarsh wetland went down to below 10 mV within 37 days likely due to the fide. The DOM before and after MFCs treatment was analyzed using the ultraviolet-visible absorption spectroscopy (UV-Vis) and the fluorescence excitation-emission matrix (EEM). Results showed that both carbon sources and anaerobic microorganisms included in subaqueous wetland sediments (SWSs) were vital for the electricity generation, and the food used to produce electrical energy mainly came from SWSs instead of wetlands water.