In order to study the effect of Potamogeton crispus decomposition on the dissolved concentrations of greenhouse gases (GHGs) and their diffusion fluxes at the sediment-surface water-air interface in the Lake Dongping, surface water and sediment core samples were collected in situ seven times from May to July in 2016, and the decomposition experiment was also carried out by using the litterbag method to explore the dynamic of the dry mass loss of P. crispus. Dissolved concentrations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) in the surface water and pore water were concurrently measured, and the diffusion fluxes at the sediment-surface water interface and the surface water-air interface were calculated by using the Fick's first law and the two-layered model respectively. In addition, the physicochemical properties of surface water and sediment were also measured to explore the main factors that might affect the concentrations and diffusion fluxes of GHGs as well as their sources during the decomposition of P. crispus. The results showed that the dry mass loss of P. crispus could be described accurately by the double exponential model which suggested two stages (rapid and slow) of P. crispus decomposition. The pH and nitrite concentrations in the surface water decreased first and then increased, while the change of the dissolved oxygen, ammonia, nitrate and dissolved inorganic phosphorus concentrations was reversed. In sediment, the ammonium content first increased and then decreased, while the nitrate content first decreased and then significantly increased, the organic matter content and pH of the sediment fluctuated. Both the concentrations and diffusion fluxes of GHGs at the water-air interface were in the order of CO₂> CH₄> N₂O, and the average fluxes were 5862.9±5441.4, 31.15±41.3 and 0.15±0.57 μmol/(m²·h), respectively. Generally, the waterbody acted as the source of the GHGs to the air, dominated by the carbon emission. The concentrations of N₂O in surface water and its diffusion fluxes at the surface water-air interface first decreased and then increased, and N₂O concentrations in pore water presented maximum values of 22.7 and 55.6 nmol/L in the rapid and slow decomposition stage respectively, while its fluxes at the sediment-water interface increased slowly in the early stage and then decreased rapidly at the end of the decomposition. For CH₄, its concentrations in the surface water and pore water and interface diffusion fluxes all dropped slightly in the initial stage and then continued to rise. The concentrations of CO₂ in surface water and its diffusion fluxes at the surface water-air interface increased continually and then decreased significantly to lower levels at the end of the rapid decomposition and then remain stable; while the concentrations of CO₂ in pore water showed large fluctuations, which diffused to pore water at the initial stage of the decomposition and to surface water at the later stage. The correlation analysis between the concentrations and diffusion fluxes of GHGs as well as the physicochemical properties of surface water and sediment suggested that water temperature was the main factor that influenced the concentrations of GHGs in surface water and their fluxes at the water-air interface. N₂O and CH₄ in the water body mainly originated from sediment, and their concentrations in the pore water was the important factor that could control the sediment-water interface diffusion; while CO₂ in the surface water had multi sources, which were dominated by the mineralization of the organic matter in surface water.