Abstract: It becomes increasingly evident that wetland degradation pressure caused by Population and construction land demand increasing in the process of urbanization. Entropy theory provides new ideas for urban expansion, land structure transformation and the research of urban wetland degradation pressure model. There are studies showing that, urban wetland shrinkage and the increase of wetland construction land will lead to the continuous decrease of land use structure spatial entropy, while it is not fair to quantify the degradation pressure of the wetland only by the spatial entropy theory. Based on the gravity declining theory in urban geography, this research will introduce the distance factors to construct the urban wetland pressure model of gravity space entropy from the land use space entropy in the area where the wetland is located, wetland area, distance from the central wetland, distance from business center. Based on the remote sensing images of Wuhan South Lake Wetlands in 1988, a vector diagram was made according to 40 sample wetlands from the lakes and wetlands around theWuhan South Lake Wetlands. The sample wetland pressure values in five periods of 1988, 1992, 1996, 2000 and 2004 were calculated and visualized with Kriging space interpolation. The results show that: (1) with the development of urbanization and the expansion of construction land, the pressure of urban wetlands is increasing year by year. (2) the smaller the spatial entropy of land use is in the wetland area and the greater the pressure is on the wetland, the faster the wetland will disappear. (3) the wetlands farther away from the Wetland Center, closer to the urban commercial center and smaller areas are more likely to die out. (4) the results of model validation based on remote sensing data indicate that urban wetlands with high pressure are more likely to suffer significant losses or die out in the next stage. The results interpreted by remote sensing images are in agreement with the results of the urban wetland pressure model calculated according to the gravity space entropy, which shows that the model can predict the evolution process of urban wetland under the urban expansion pressure. The construction of the model is of great significance to the dynamic change and protection planning of urban wetland. Understand and grasping the loss process and trend of wetland, and predicting the evolution process of urban wetland under the pressure of urban expansion can provide direction and guidance for city manager protecting the urban wetland.
Key words：urban wetland; gravity-spatial entropy; pressure model; urban expansion