The study of vegetation background has become preliminary and infrastructural work toward the ecological environment construction in arid and semi-arid area of northwest China. Potential vegetation, as a final state of succession when one vegetation achieves the balance with its site, is the climax vegetation type at the site without human interference characterizing with high stability and full mature, and is the trend of the regional existing vegetation development. It has great significance regarding to the rehabilitation and reconstruction of vegetation in a region. Based on the integrated orderly classification system of grassland (IOCSG) and the support of GIS, this paper analyzed succession process of potential vegetation in arid and semi-arid area of northwest China. Annual precipitation from 119 meteorological stations and >0℃ annual cumulative temperature from 115 meteorological stations in northwest China during the period from 1961 to 2005 are provided by meteorological bureau in Gansu province. The conclusions are as following. Complicated processes of succession of the potential vegetation happened due to climate change in the study area. The types of the potential vegetation reduce 40% from 10 to 6 types in 1961-1975 due to climate change in the study area. The study on the variation of the distribution area of potential vegetation, which is selected to represent the transformation between the different types and their quantitative characteristics, show that there existes three typical variation patterns, i.e. steadily reducing, steadily increasing and fluctuanting. In view of the change of the geographic distribution pattern and the development direction of potential vegetation types, significant succession develop in the following sub-regions, including Turpan basin, Northern Xilinguole Plateau, Hulunbeier Plateau, and Taipingling Region. Differences exist in the succession developing direction and the spatial variation of the potential vegetation. Driving factors of potential vegetation succession is climate change. The change of the hydrothermal conditions, which directly affect the distribution of vegetation, cause the changes of the potential vegetation succession.