Abstract: Abstract: Urbanization is one of the inevitable processes due to economic development and rapid population growth. It has been an important component of land use and land cover change. This study investigated the spatial-temporal change of land use and land cover in Urumqi based on grid cell approach. Urumqi is the capital and the centre of culture, economy and transportation in Xinjiang Uyghur autonomous region, located in north-western China and characterized by an arid landscape. By using Landsat images from 1990, 2000 and 2011, land use and land cover information on Urumqi city were extracted. The land use and land cover data were apportioned to the grid cells with the size of 250 m×250 m per cell to quantify the area and percentage of change in land cover types in each cell. The sum of the land cover type area of all pixels that overlaid with the cell was divided by the area of the cell as the percentage of a land cover type within a cell. The land use and land cover vector maps of Urumqi city were then drawn. Based on these vector maps, the proportion of each land cover category within a grid cell area were calculated. Finally, we analyzed the spatial-temporal changing characteristics of land use and land cover of Urumqi city from 1990 to 2011 and its driving factors using the proportional land cover maps. The transforming and replacing relationship between different land cover categories were analyzed as well based on the correlation and regression methods. The result showed that: 1) from 1990 to 2011, Urumqi city experienced rapid expansion. A large amount of bare land and green land were converted into construction land. The construction land increased from 157.37 km2 in 1990 to 444.89 km2 in 2011. The bare land declined continuously from the percentage of 75.13% in 1990 to 49.79% in 2011. The green land had slight decline in 2000 and then increased to 402.80 km2 in 2011. The water body was slightly increased. 2) Land use and land cover showed different changing trends in different area and directions within the study area due to the impacts of topography, policy, urban planning, road system and so on. 3) The correlation between change in the construction land area and that in the bare land area was negative about -0.7 and that between that in the construction land and the green land was about -0.2. The correlation between green land and the bare land was about -0.5. Thus, the change in construction land area and green land area was caused by the bare land area change. Based on the grid cell approach, we cannot only analyze the overall changing characteristics of land use, but precisely quantify the spatial-temporal changing characteristics of different areas and directions within the study region and its driving factors. The data based on the grid unit can better provide valuable information for the current urban development in Urumqi and can better predict the future urban development.