Although more and more people realize the important role of the urbanization process on the economic, political and environmental systems along the Belt and Road, the study on urban expansion and form changes is still limited. Based on the latest 300 m resolution global land cover dataset from 1992 to 2015 released by the ESA Climate Change Initiative project, DMSP/OLS night lighting data from 1992 to 2012, and LandScan population data from 2000 to 2015, in this paper we first analyzed the spatial pattern of urban land growth and dynamics in the ten major sub-regions along the Belt and Road from 1992 to 2015. Then, by analyzing the spatial and temporal changes of urban land density in concentric rings in 1992, 2003 and 2015, the expansion and form changes of 80 cities along the Belt and Road were quantified. Finally, the long-term relationships between urban land area, weighted lighting area and urban population were quantified by using three statistical models, including linear, power-law and exponential function models. The results show that the urban land area along the Belt and Road increased from 0.24% in 1992 to 0.56% in 2015, and developing countries in Africa and Asia are major contributors. The density of urban land in the concentric rings is decreasing from the city center to the urban fringe, and the spatial distribution between cities is completely different. Comparisons among cities in China, Europe, Africa, West Asia, Southeast Asia, and India with populations of more than one million, show that, in addition to the decentralization of China's urban form, the overall urban form of other sub-regions became compact. Further analysis results show that the urban economic vitality and urban population distribution trends will affect the urban spatial expansion and form changes at different levels.