Land use change, an important factor affecting global environmental change, is one of the most crucial human activities. Research on land use change is critical to reveal the mechanism of impacts of human activities on land resources. In this study, we used the ArcGIS spatial analysis function and the SPSS principal components method to analyze the spatial and temporal changes of land use in the Southeastern River Basin (including Taiwan) from 1990 to 2015 and explore the possible driving mechanisms. The main results are as follows:(1) From 1990 to 2015, the proportions of different land types throughout the basin was forest land > farmland > grassland > urban and rural construction land > water area > unused land. Forest and cultivated land largely gather on the north of the basin, while they are more scattered and less in the south. Urban and rural construction land is concentrated in the coastal areas of Taiwan province, where the economy is relatively well developed, as well as in the northern basin near the Yangtze River Delta. (2) The comprehensive dynamic degree of land use in the basin is 0.68%, and the degree of conversion of overall land use type first declined and then increased from 1990 to 2015. Most changes occurred on urban and rural construction lands and cultivated land. Land usage change in the southern region of the basin is more intense than that in the north. The main type of land use change in Taiwan province was cultivated land and urban and rural construction land. The comparison of changes in the area of land types in the basin is:urban and rural construction land > cultivated land > grassland > forest land > water area > unused land. The most significant increases in urban and rural construction comes from cultivated land. Hence, the increases in cultivated land begins with forest land and then gradually transitions to urban and rural construction land. There is a certain degree of synergy between the intensity of urban land use and cultivated land. The latter has maintained a large degree of change and dominates the changing structure of each period. The average annual dynamics of other construction land in the past 25 years was 17.30%, showing clear growth trends. (3) The main driving forces behind urban and rural construction land usage changes in mainland China are population quantity and structure, urbanization level, and level of social and economic development. On this basis, Taiwan province has increased the social industrial and agricultural industrial structure adjustment factors. Additionally, the main driving forces behind changes in cultivated land in mainland China are population size and structure, urbanization level, and social and agricultural industrial structures. In Taiwan province, the social and agricultural industrial structures and agricultural production levels are the main forces driving changes in cultivated land. In this study, we analyzed the spatial and temporal variability and driving mechanisms of land use changes in the southeastern river basins. This study provides theoretical support for the rational planning for land resources in the region, and provides baseline data support for the comprehensive management of resources and the environment at the basin-wide scale.