Spatial and temporal variations of seasonally frozen ground extent have important impacts on carbon exchange between the atmosphere and the land surface, surface energy balance, hydrologic cycle, and ecosystems as a whole. By using air temperature and soil temperature at 5 cm depth from 11 meteorological stations for more than 40 years, we established a relationship between mean monthly air temperature and numbers of frozen days within the month. Based on this relationship, grid air temperature data with a resolution of 5 kilometers, and 30m-DEM data, we mapped the monthly seasonally frozen ground distribution over the Heihe River Basin, and three different types of freezing/thawing status can be divided by using the spatial characteristics : complete frozen, incomplete frozen, and not frozen. The results indicate that the maximum area of three different types of soil freezethaw status occur in January, November, and June or July respectively. Over the study period from 2000 through 2009, interannual variations of the complete frozen area extent is large in cold season, vice versa in warm season; there is a huge change in the warmer and catathermal period for incomplete frozen area extent; not frozen area extent has a huge variation in April and October. The maximum of freezing probability occurs in January, while the minimum of probability occurs between June and July. To the spatial perspective, distribution and variation of monthly seasonally frozen ground and freezing probability are mainly controlled by elevation, following by latitude over the Heihe River Basin.