Interspecific pattern and competitive relationship of plant community has changed in Yancheng coastal wetland, resulting in the change of wetland landscape structure and pattern. Using TM images of long time series with the help of GIS technology, the spatio-temporal change characteristics of plant community pattern and competitive relationship were analyzed by landscape ecology method from 1992 to 2017, in the core area of the Yancheng National Nature Reserve (YNNR) in Jiangsu Province. The results were as follows. ① From 1992 to 2017, the Phragmites community and Spartina community expanded continuously, with the area percentage reaching 37.06% and 34.50% respectively by 2017. The Suaeda community showed the characteristics of continuous shrinkage as a whole, with only 5.09% by 2017. ② From 1992 to 2017, the values of SHDI (Shannon's Diversity Index) and ED (Edge Density) first increased to 1.482 and 14.391, and then decreased to 1.283 and 11.967 respectively, which reflected the trend of interspecific competition from simplification to diversification and then to simplification. ③ From 1992 to 2017, the spatial position of interspecific competition of Phragmites-Suaeda community firstly advanced to the ocean and then retreated to the land. The position of interspecific competition of Suaeda-Spartina community firstly evolved to the sea, then the land and then to the sea. The position of interspecific competition of Phragmites-Suaeda-Spartina community evolved from the south to the middle part of the region. This study can be used to further understand the basic structure and dynamic trend of plant community in coastal wetland. It provides scientific reference for biodiversity conservation and restoration.