The urban area expansion is an important indicator for measuring urbanization level.Based on three Landsat MSS images

ten TM images

one DMC data and one "Beijing-1" small satellite data obtained in 2005

the urban built-up characteristic of Beijing and its impact on the peripheral land during 1973—2005 were analyzed.The urban area was 183.84km2 in 1973 and increased to 1209.97km2 in 2005

the built-up area was increased by 1026.13km2 during the past 32 years and expanded 32.07km2 per year.The built-up area was expanded around the old area and didn’t present manifest change in a certain direction.The expansion rate was distinct from each other and Beijing city was experienced two fast expansion stages comparatively.The increased built-up area originated from different land use type

of which about 54.34% converted from rural area and dependent factory

diggings land and other construction area.The other mainly came from arable land that account for 43.57% of the whole added built-up area.Many factors contributed to the urban land use changes.But four major driving forces

population growth

economic increase

transportation infrastructure improvement and institution and policy change

were the most important factors.Population growth can simulate the built-up area manifestly

the economic increase was the main impetus of the land use

the transportation infrastructure improvement was the impetus for the urban expansion

while policy change determined the macroscopical development and expansion pattern in some degree.