Abstract: The Three-North Shelter Forest Program is a key forestry ecological project in China. The quantity and spatial distribution of the shelter forest in the program affect the ecological environment of the entire Three-North region. In this paper, multisensor remote sensing data were used to scientifically, objectively and comprehensively estimate the quantity and spatial distribution pattern of the shelter forest in this region in 1978-2008. Firstly, the Landsat TM images (30 m in resolution) were adopted to extract the shelter forest data in this region in 2008. Then, based on random sampling techniques, the calibration formulae for the shelter forest area in different precipitation climate regions estimated by the SPOT5 (2.5 m in resolution) and Landsat TM were constructed. By using the above-mentioned results, the shelter forest area in the ThreeNorth region in 2008 was estimated. In 2008, the total area of the shelter forest (canopy density of arbor shelter forest was >0.3, coverage of shrub shelter forest was > 40%, and accuracy was about 85%) in this region was 328360.03 km², with 116244.55 km² in Northeast China, 42981.32 km² in North China, 76767.05 km² in Loess Plateau, and 92367.11 km² in MongoliaXinjiang Region. According to the classification of shelter forest types, the areas of coniferous forest, broadleaved forest, mixed broadleafconifer forest and shrubland were 62614.74, 121628.51, 22144.09 and 121972.69 km², respectively.