Abstract: To study the changes in soil moisture and temperature during a freezing-thawing period ,the space-time change law of soil moisture and temperature of different soil depth layers were analyzed by monitoring the soil moisture and temperature data of different land use runoff plots in the field. The relationship between soil moisture and temperature in the study area was then clarified. The results showed that the variation degree of the 20 cm soil layer in sloped farmland was the largest,while the strongest active layers in the grassland and woodland were 30 cm and 10 cm,respectively. The 20 cm soil layer in the sloped farmland had the largest dispersion of water content,while the active layers in grassland and forestland were 30 cm and 10 cm,respectively. The grassland first entered the freezing period and the thawing period,and freeze and melt time lags layer by layer,and the soil moisture content and temperature of the three land types followed quadratic functions. The hydrothermal relationship of the soil in forestland was the strongest,which is more conducive to the soil water-heat retention in the loess area. This study provides a scientific basis for the research of soil moisture on vegetation restoration and the protection of the environment from construction in the loess area.

Key words: freezing-thawing period, land use, soil moisture, soil temperature, correlation, Ansai County