Exogenous sulfate (SO₄^2-) resulting from human activity, can strongly influence the emission of methane (CH₄) from wetland ecosystems. Previous studies have reported the suppression CH₄ emissions of peatlands and paddies by cumulative SO₄^2- deposition in simulated acid rain conditions. However, very few studies have presented data on the effect of the addition of SO₄^2- on CH₄ emissions in estuarine freshwater tidal wetlands. In this study, the effect of simulated deposition of SO₄^2- on the CH₄ emissions was examined by manipulating SO₄^2- inputs to a Sagittaria trifolia-dominated freshwater tidal wetland in the Tajiaozhou area of the Min River estuary from December 2015 to October 2016. Monthly pulses of dissolved K₂SO₄ were applied over one year at doses of 60 and 120 kg S hm^-2 a^-1 (abbreviated as S-60 and S-120, respectively), and CH₄ fluxes were measured at regular intervals using a static chamber/gas chromatographic method. On the annual scale, the average CH₄ emissions from the control, S-60-and S-120-amended plots were 7.88±1.00, 6.55±0.97 and 6.66±1.49 mg h^-1 m^-2, respectively. Thus, the two addition treatments did not significantly decrease the CH₄ emissions from S. trifolia-dominated freshwater tidal wetland, which is different from the effects of simulated SO₄^2- deposition on the CH₄ emissions from peatlands and paddies in other reports. The S-60 and S-120 treatments significantly increased the pore water SO₄^2- concentrations at a depth of 10 cm in the S. trifolia wetland at an annual scale as well as in autumn and winter. CH₄ emissions in summer and autumn were significantly higher than those in winter and spring. CH₄ emissions from the control, S-60-and S-120-amended plots demonstrated significant positive correlations with soil temperature. These results indicate that soil temperature is an important environmental factor affecting the temporal variation of CH₄ emission from a subtropical estuarine freshwater tidal wetland.