Abstract: As an important part of ecosystem, wetland plays a significant role in maintaining regional ecological security. Based on the Landsat remote sensing image data in 1975, 2000 and 2018, the interpretation data of wetland during the three periods are obtained to analyze the spatiotemporal variation of wetland in Songnen Plain in nearly 50 years with the methods of dynamic degree, difference analysis and transfer matrix, which provides certain theoretical basis for the research and protection of wetland ecosystem in Songnen Plain. The results reveal that the wetland area shows an overall increasing trend from 20 189.81 km² in 1975 to 29 456.79 km² in 2018, manifested by the substantial decrease of natural wetland during 1975-2000 and large-scale increase of constructed wetland during 2000-2018. It is concluded that water storage project, floodwall and wetland reclamation are the main factors causing the decrease of natural wetlands, followed by precipitation reduction, temperature rise and evaporation increase. Driven by the economic benefit, the paddy field reconstruction and expansion mainly contributes to the increase of constructed wetlands.