Estuarine tidal marsh is one of the coastal blue carbon ecosystems in the world. Sea level rise and nitrogen enrichment are two major global environmental issues facing by estuarine wetlands. In recent years, meteorological drought events often occurred. The influences of drought, and combination of drought and sea-level rise, and nitrogen enrichment on net ecosystem exchange (NEE) of CO₂ of estuarine tidal marshes remain poorly studied. A novel approach using the weirs for in-situ manipulating sea level rise (including the increase of depth and duration of flooding) at relatively larger spatial scale was developed in the journal of Methods in Ecology & Evolution, however at present, the method has not been actually used in-situ to study effects of sea level rise on carbon cycle in coastal tidal marsh ecosystem. In our study, we improved the weirs and used them to manipulate the sea level rise (SR) treatment in-situ, and meanwhile applied in-situ experimental manipulations of control, nitrogen enrichment (NE), and SR+NE in a tidal brackish marsh of Cyperus malaccensis in the Minjiang River estuary, southeastern China. In summer and autumn of 2020, the meteorological drought occurred in the coastal zone of Fujian Province, which provided an opportunity to determine the effects of drought, the combination of drought and simulated sea-level rise, nitrogen enrichment on the NEE and ecosystem respiration (ER). From August to October in 2019 and 2020, the NEE and ER were measured using transparent static chamber (or black cloth shading)+Licor-6800 method. Compared with 2019 (normal year), the NEE under each treatment (including control) was significantly reduced in 2020 (drought year), and the ER in the control, the SR, and the NE was also significantly decreased in 2020. NEE was significantly negatively correlated with the photosynthetically active radiation (PAR). The results indicate that drought event can reduce net CO₂ gain in estuarine tidal marshes, and this decrease still occurs under combination of drought and sea-level rise, nitrogen enrichment.