Understanding changes in the landscape pattern of built-up land its driving factors not only helps to solve the eco-environmental problems in cities but also provides a scientific basis for urban land use optimization and landscape planning. In this study, we used multi-source data (e.g., 30 m resolution Landsat images and statistical yearbooks) to analyze changes in sprawl mode, morphology and landscape pattern of built-up land in a rapidly urbanized medium-sized city-Yangzhou City, Jiangsu Province, China. Furthermore, we employed the boosted regression tree method to quantify the effects of geographic and socioeconomic factors on landscape patterns of the built-up land, which revealed changes in the driving factors with the built-up land sprawl. The results showed that the area of the built-up land gradually increased from 1995 to 2015. All of the three sprawl modes (infilling, edge-expansion and leapfrog) appeared in each period, but their relative dominances varied with the built-up land sprawl. The morphology of the built-up land underwent an alternating process of "diffusion" and "coalescence", while the landscape pattern tended to homogenize (i.e., decreased fragmentation and increased aggregation of the built-up landscape). Geographical factors (altitude and distance from the geographical center of a county) played more important roles in shaping landscape pattern than socioeconomic factors. Moreover, the combined effects of geographical factors decreased with the built-up land sprawl, while socioeconomic effects became more significant. Landscape fragmentation of the built-up land increased with increasing altitude and population density and decreasing total population; meanwhile, the landscape aggregation was inhibited. However, effects of other factors (i.e., distance from the center of a county, GDP per capita, and the proportion of secondary industry) on landscape pattern varied with the built-up land sprawl. For example, the promoting effect of GDP per capita on landscape fragmentation turned to an inhibiting effect, while the inhibiting effect of secondary industry turned to a promoting one.