To better understand the Sulfur (S) cycle in the wetland ecosystem, the S cycle and its compartmental distribution within an atmosphere-plant-soil system were studied using a compartment model in the Calamagrostis angustifolia wetland in the Sanjiang Plain, Northeast China. The results showed that the soil was the main S storage and flux hinge in which 97.78% S was accumulated. In the plant subsystem, the root was the main S storage, and it remained at 79.60% of the total S contents, which in the Calamagrostis angustifolia wetland ecosystem showed that the parts above the ground took up 0.75 g S/m², the S re-transferring biomass to the root was 0.24 g S/m², and to the litter was 0.51 g S/m²; the root took up 3.76 g S/m² and the S transferring biomass to the soil took up 3.07 g S/m²; the litter S biomass was 0.75 g S/(m²·a) and the S transferring biomass to the soil was more than 0.52 g S/(m²·a). The emission amount of H₂S from the Calamagrostis angustifolia wetland ecosystem to the atmosphere was 1.42 mg S/m², whereas carbonyl sulfide (COS) was absorbed by the Calamagrostis angustifolia wetland from the atmosphere and the absorption amount was 1.83 mg S/m². The S input biomass from the rain to the ecosystem was 4.85mg S/m² during the growing season. The difference between input and output amounts was 5.26 mg S/m², which indicated that S was accumulated in the ecosystem and would lead to wetland acidification in the future.