Border area is not only an important gateway for inland opening-up, but also an critical part in the building of a moderately prosperous society and optimizing national urban spatial pattern in China. Due to the location, natural resources endowment, and traffic accessibility, the urbanization development is relatively slow in border areas. Therefore, border area is a special area that should be given close attention, especially under the background of the Belt and Road Initiative and China's regional coordinated development program. Based on the county-level data from 2000 to 2015, this paper tries to analyze the spatio-temporal pattern of urbanization in 134 border counties, and applies the geographical detector method to study the driving forces of urbanization in border areas. Conclusions are as follows: (1) From 2000 to 2015, urbanization rate in border areas was lower than the national average, and the gap was widening. Some border counties in southern Xinjiang, Tibet, northeast of Inner Mongolia, and Yunnan, are even facing the problem of population loss. (2) In the same period, urbanization rate in the northwestern and southwestern borders is low, but it grows relatively fast compared with other border counties; urbanization rate in Tibetan border area is the lowest and grows relatively slowly; urbanization rate in the northeastern and northern border areas is slightly higher, but it grows slowly or even stagnates. (3) Transportation and industry are the important driving forces of urbanization in border areas, while the driving forces of market is relatively weak. And there are obvious mutual reinforcements among the driving forces, while the effort of resource force increases obviously after interaction. (4) Urbanization rate in the northwestern and southwestern border areas grows relatively fast, with industrial power and transportation power, market power and administrative power as the main driving forces. Tibetan border area has the lowest urbanization rate and growth rate, as the driving force of urbanization with strong contribution has not yet formed in Tibet. In the northeastern and northern border areas, the contribution of transportation power to urbanization is greater than that of other forces, and its interaction with market and industry has obvious effects on urbanization.