As urban development has a great impact on land use, it is an important driving force for land use change. Landsat remote sensing images of Haitan Island in 1984, 1990, 1996, 2003, 2010, and 2017 were taken as data sources for defining land use categories by random forest to study the impact of the development of Pingtan Comprehensive Experimental Zone on land use. Land use changes, urban expansion and its influence on other land types in 5 periods were quantitatively analyzed. Results show that under the premise of feature variables optimization, the classification accuracy of each period is higher than 85%, meeting the requirements of subsequent analysis. Besides, the area of farmland in each period is the largest, followed by that of woodland (including forest and shrubland), and bare land has the smallest area. The overall farmland showed a decreasing trend, with the largest reduction in 1984–1990 (8.07%). Construction land expanded in all six periods, with the maximum expansion from 2010 to 2017 (11.82%). Moreover, urban expansion in each period was dominated by edge expansion, followed by leapfrog expansion and then infilling expansion.The development of cities on the island has a major driving effect on the changes of other land types, and the main source and destination of urban expansion are farmland. The main transformation modes of urban land include farmland, woodland, grassland, and wetland.