Upon the experimental study by using methods of equilibrium vapor pressure and differential thermal analysis,the distinguishing features of adsorption and desorption isotherms of the gaseous water in soil at 20℃ and 30℃ and the characteristics of desorption heat of the adsorbed water are discussed in the present paper.The results are shown as follows:1.When the relative vapor pressure reached to 72-75%,capillary moisture condensation began to appear in the tested soil.2.Besides the clay content,specific surface area and organic matter content of soil,temperature also affected the amount of gaseous water adsorbed in soil,and the amount of residual water in samples of desorption equilibrium at 30℃ was more than that at 20℃ while the moisture content of adsorption equilibrium samples at 30℃ was less than that at 20℃ in the general range of the relative vapor pressure.3.A hysteresis effect existed between the adsorption and the desorption of soil water vapor,and its extent showed a consistent order with the clay content and specific surface area of soil.The hysteresis effect also strengthened with increasing temperature.4.The partial molar desorption heat of the adsorbed water at very low soil moisture content was far higher than that at high soil moisture,suggesting that it mainly depends on chemical adsorption for dry soil to adsorb water vapor molecules at the initial stage.